Pros: One seat from convertable through booster
Cons: Big in small cars
Heavy if you have to move it often
I wish they had this seat 5 years ago when I was first in the market for convertible car seats!! This is the best one I've used thus far!
We purchased this recently for my 4th child a large toddler who is rapidly outgrowing his traditional covertable seat (Evenflo Triuph) due to his weight nearing the 40 lbs mark. And while neither car seat is light or small, I love the features of this seat- the high weight limit for harness, the ability to use as a high back then low back booster- AWESOME! For my first kids, they went from the infant seat to the convertible to the high back boosters.. and if you add up the costs, I spent far more on the 3 separate options than if I went from the infant seat to the Nautilus. In theory, you could go from the 30 lbs weight limit Graco Safe Seat to this one and skip the traditional convertible seat entirely.
For those of you who aren't really familiar with car seat safety- the longer you harness your child, the safer they are. So, even if you have a 30+ lb child, it's not always (or often) a good idea to move to a booster seat. The longer they're in a harness, the safer they are in the event of a crash (not to mention that you KNOW they're correctly buckled, whereas the booster lets the kids move the seat belt incorrectly, wiggle around, hit their siblings.. )
But the other part of safety is- the longer they are rear-facing, the safer they are, so this seat really is the best option once your child is ready to be forward facing- NOT before a year and really, it would be safer to turn them to forward facing at 30 lbs. It was a little disappointing that this seat can't be rear racing, as I love the thought that it could be our only seat purchased for a child.
Thus enters the higher weight harness seats. I have also used the Sunshine kids Radians and those DO have a smaller footprint, meaning if you need to get 3 car seats in a row, it will be a better option for you. My kids didn't find it as comfortable and it costs more than the Nautilus. The Radian can be installed rear-facing.
The Nautilus is not a small seat by any means. It dwarfs all our other seats- the Evenflow Triumph and our cheap costco backup seat and the high back Graco Turbo boosters in both width and height. It makes sense realizing that your 9 year old will fit in it, but when I first took it out of the box I was a bit surprised.
And it's heavy. But I rarely have to drag my carseats around, so it isn't a big problem. It IS a hassle when you're transferring car seats from your car to another, but really any car seat will be- if it's 10 lbs or 30 lbs. I have 4 kids in seats/boosters, so it's not convenient no matter how you slice it. We did use our cheap light costco seat when flying, I can't see myself lugging the Nautilus through the airport, but we could with one of those luggage carts fairly easily.
Other pluses- farily easy to clean. A big plus for those of us with car sick kids. (The Evenflo Tripumph is a nightmare to clean since you cannot get the straps off the seat.) The straps come off and are not super easy to re-thread, but something you have to do to move the straps up, anyway. You do have to un-install the carseat to adjust the straps- say you realize your child needs the next higher ones, you have to uninstall it, un-thread them and then re-thread them over those little roller things. Not super easy. The Triumph's are much easier to flip the seat flap forward, the plastic cover forward, pull the pastic tabs and adjust the straps , slide the straps in the corresponding slot and have kid buckled in carseat in 2 minutes or less. Not that normal people need to adjust the straps often, but it's nice to know you can do it quickly.
Sleeping- it does recline some and I've had 2 different kids fall asleep in it, so I don't see sleeping in it an issue- they tilt their head back and to the side and lean on the head rest. It does not recline as far back as traditional convertible seats do.
The crotch strap- I haven't had a problem or complaint about it from either the 4 year old girl or 2 year old boy who have used it. We found that strap too short in the Radian- lots of complaints on it, especially when the harness was tightened correctly.
Installation- I haven't tried using the Latch installation, as our vehicle doesn't have Latch in all seat locations. Installation with a seat belt in a Chevy Venture or Ford Explorer was standard.