Diono Monterey 5ist high back booster review

Diono Monterey 5ist fully extended

The Diono Monterey booster seat has been a solid booster option for kids since it was first released in 2008. Some of our earliest CSFTL models rode in Montereys, today they’re getting ready to drive! The Monterey’s high top shoulder belt guide, combined with the adjustable width allowed it to accommodate growing children nicely, and gave bigger kiddos some extra width so they were comfortable (and not feeling squished).

The latest version of the Monterey, the 5ist, looks like a slimmer version of the previous versions of this booster. We’re interested to see how that translates fit-wise, since the width of the Monterey has always been a selling point. Let’s take a closer look at the Diono Monterey 5ist that is now available in the USA and Canada.

Diono Monterey – 5ist, 4DXT, and XT in smallest settings

Previous versions of the Diono Monterey featured a dial on the back of the seat that allowed the back to be adjusted to wider settings as the child grew. The width adjustments were never required. Some children needed the extra width as they grew taller and some did not.

Diono Monterey – 5ist, 4DXT, and XT in largest settings

The Diono Monterey 5ist does not have this feature – instead the back widens as the headrest (and shoulder belt guide) is moved up. This results in the seat automatically becoming wider as it is adjusted taller. It also means that anyone purchasing the seat will need to ensure that the seating position can accommodate the full 23 inch width if they want the Monterey 5ist to be able to fit in all headrest positions in their vehicle.

Diono Monterey 5ist cup holder

The Diono Monterey 5ist comes with one removable cup holder that can be attached to either side of the seat (or not used at all). It slides into the plastic slit on the side of the seat, and clicks in easily. Once attached properly. it nestles firmly in place and will not fall out (if it IS falling out, you have not pushed it far enough into the booster).

Folded Diono Monterey 5ist

The Diono Monterey 5ist does not convert to a backless booster like previous versions of the Monterey do. Instead, it features a folding function and comes with carry straps that basically turn the Monterey 5ist into a booster backpack.

To carry the Diono Monterey 5ist as a backpack:

• Fold the Monterey 5ist by pulling on the seat fold lever under the front end of the booster seat
• Remove the carry straps from the carry strap storage compartment on the back of the Monterey 5ist
• Attach the carry straps hooks to the top and bottom loops on the back of the seat
• Adjust the carry straps to a comfortable fit by moving the slider up or down
• Place straps over your shoulders to wear the Monterey 5ist on your back

Diono Monterey 5ist in the smallest setting

There is a warning in the manual to not use the carry straps if suffering from back, shoulder, or neck problems. Because this seat weighs almost 20 pounds, carrying it as a backpack isn’t a terrific option for most children who might use it in a carpool situation. Kidshealth.org recommends that children not carry more than 20% of their body weight, which means that to safely carry the Diono Monterey 5ist as a backpack, the child needs to weigh at least 92.5 pounds (well over the 40 pound minimum of the booster). Even for an adult, carrying 20 pounds of anything can get pretty heavy!

YELLOW rigid lower anchors on the Diono Monterey 5ist

Previous versions of the Diono Monterey have featured Diono’s classic upside-down lower anchor connectors. The Monterey 5ist is the first version of the Monterey to not only feature premium lower anchors (in yellow), but also rigid lower anchors, which Diono refers to as ISOFIX connectors in their manual. Note: the term ISOFIX isn’t used in the United States or Canada, our versions are LATCH or UAS, respectively but the manual for this seat refers to ISOFIX.

Diono Monterey 5ist shoulder belt guide

Diono has introduced a new shoulder belt guide on their Monterey 5ist. It’s enough of a departure from other belt guides on other Diono booster seats that we felt it it earned its own section.

The shoulder belt guide requires that the front metal piece be pushed out of the way when threading the vehicle shoulder belt through the guide, and locks itself in place when released. This prevents the shoulder belt from being able to slip out of the guide. Because the shoulder belt guide itself is nice and open, this may be a good solution for vehicles with odd seat belt geometry that is prone to slipping out of the shoulder belt guide of other high back boosters.

Diono Monterey 5ist headrest adjuster handle

To adjust the Monterey’s height, squeeze the head support adjuster and move the headrest up or down. Because the headrest adjuster also adjusts the width of the back of the seat, it is not a smooth or easy adjustment and sometimes requires two hands (especially if adjusting in the vehicle).

Diono Monterey 5ist – 5 year old

Our 5 year old model is two months shy of her 6th birthday and has been begging us to try a booster seat. She is 46 inches tall and weighs 45 pounds. We’ve decided that this would be a good opportunity to practice sitting properly in a booster seat, so the Monterey 5ist replaced her regular harnessed car seat for a couple of weeks of short drives to see if she has the maturity to sit properly in a booster seat.

The second time she used the Monterey 5ist, she fell asleep in the booster. We were surprised and happy to see that she was able to maintain a safe seating position in the booster seat. The supportive sides and headrest helped keep her upright despite being fast asleep (summer camp is tiring!).

When not sleeping (and even when sleeping) the seat belt fit on this model is excellent. This fit is on par with what we have come to expect from the Diono Monterey, and we’re glad to see that it’s still consistent. The lap belt is low on her hips, touching her thighs, and the shoulder belt is centered on her shoulder.

Diono Monterey 5ist – 8 year old

Our eight year old model stands 53 inches tall and weighs 63 pounds. She absolutely loves blue car seats and booster seats. She was eager to try the blue Diono Monterey 5ist.

She found the lack of arm rests made the booster easier to buckle than her Monterey XT (also in blue, of course). We see that the seat belt fits her beautifully in the Monterey 5ist – the shoulder belt is centered on her shoulder and the lap belt is low on her hips.

Diono Monterey 5ist – 9 year old

Our nine year old model stands 56 inches tall and weighs 90 pounds. His everyday seat is the Diono Monterey 4DXT and he will likely fit that version of the Monterey until he passes the 5 Step Test (which will be soon).

We have extended the Monterey 5ist to the highest position and our nine year old model just barely fits in the booster seat. He didn’t say anything negative about the booster, but did ask when he could switch back to his other seat. Given that the 5ist has a higher MSRP than the 4DXT, we are a bit disappointed to see that the 4DXT lasts longer (likely by a year in high back booster mode, on average).

Diono Monterey 5ist bottom of seat

FAA Approval: Like all booster seats, the Diono Monterey 5ist requires a lap/shoulder belt to use, so therefore it is not FAA approved for use on aircraft.

Expiration: The Monterey 5ist expires 8 years from the date of purchase. The label with the model number and date of manufacture is on the bottom of the seat. The expiration information is located in the manual.

Manual Storage — the manual storage location is easier to find on the Monterey 5ist than on the previous versions of the Monterey. There is a storage door that is clearly labelled with a picture of the manual on the bottom of the booster seat.

Date of Manufacture (and National Safety Mark for Canadian users) — located on the bottom of the seat.