Diono Monterey 5iST FixSafe

The Monterey 5iST is a highback-only booster, meaning that the seatback does not have the option to come off to be used in backless mode. CR recommends highback boosters for everyday use because they typically position the shoulder belt better on a child, provide some side-impact protection, and offer a more comfortable place for resting children to lay their heads. Once your child outgrows their forward-facing child car seat by weight or height, CR and the American Academy of Pediatrics (AAP) recommend that kids use boosters until they are at least 4 feet 9 inches tall, are 8 to 12 years old, and have the developmental maturity to keep their belt properly positioned for an entire car ride.

While heavy and bulky at 19 lbs, the Diono Monterey 5iST comes with a carrying strap and can be folded once the cupholders are removed. This foldability could be handy for travel or for storing the seat.

The 5iST is a balanced performer for both belt fit and ease of use. Diono does recommend securing the booster with the rigid LATCH when available.

At 23 inches across, the Monterey 5iST is a very wide booster that may overlap with vehicle belt hardware and contact interior trim or the head restraints in adjacent seats. The width of this booster may also present a challenge for families that need to fit three car seats across the back seat. 

The Diono Monterey 5iST FixSafe is part of the Car Seats test program at Consumer Reports. In our lab tests, Booster Seats models like the Monterey 5iST FixSafe are rated on multiple criteria, such as those listed below.

Booster fit (with back): A rating that reflects a booster seat's ability to correctly position the lap and shoulder belts in various test vehicles using a child-sized dummy, when used as a highback booster. Additionally, it includes an assessment of the booster's compatibility with vehicle seats and interior components.

Booster fit (no-back): A rating that reflects a booster seat's ability to correctly position the lap and shoulder belts in various test vehicles using a child-sized dummy, when used as a backless booster. Additionally, it includes an assessment of the booster's compatibility with vehicle seats and interior components.

Ease of use: Our evaluation of how easy each seat is to use, including items such as the clarity of labels and instructions, the ease of achieving an appropriate belt fit, and the transition between highback and backless modes where applicable.