I think the seat would be comfortable enough as the padding feels great, but I won't know for awhile.
The straps will not fit around my canoe seat. They are a couple of inches too short. I searched all over the internet and found two things. 1. This is a very common complaint about this seat and has been posted by many people on many websites for a long time. I assume the manufacturer must know about it and has chosen not to fix it. 2. There is only one place I can find the SitBacker extension straps, and that happens to be the GCI website. I've searched all kinds of other outdoor stores and Amazon without luck. The straps are 10 bucks on their website, but have an additional 8 or 9 dollar shipping cost. That's ridiculous. When I spend this much money on a seat, I don't expect to have to drop 20 more dollars to make it fit. I also don't expect to have to rig it with bungees, but that looks like that will be my only option.

I have been paddling canoes for almost 60 years. I used to sneer at people who used canoe seats. Until I got a little older and the cumulative affects of work gave me the back miseries. My wife got this for me and now I would not canoe without it. Velcro straps secure it to the canoes seat. The back position is adjustable with straps and the back fold down when not in use. It is possible that this seat may not fit some oversized canoe seats.
Bracing yourself against the seat back may actually make your paddling more efficient.
Well made, I would expect this to last 20+ years

I have used an REI Trail Chair ([...]) for hundreds of miles on the water and many nights on the ground. That chair is very durable. I bought the GCI chair because I wanted more bottom cushion and the ability to clip the chair to a canoe seat. The shock corded back pocket is also a nice feature for securing small items. The bottom and back cushions are comfortable.
The only complaint I have with the chair is the bottom cushion two-piece design. I bought two of these chairs and both ripped the same way during the first canoe trip. If you buy this seat be careful reclining. I imagine that reclining places more weight at the back of seat cushion which pushes the seat forward causing the stitching to flex too much and rip (see picture). I think that a single piece cushion design would not have this problem.

I'm an avid canoeist and as I get older, my back likes to have support. I had a folding 'crazy creek' type chair that I used, but it wasn't really designed for canoeing and kinda sagged too much to be useful. This chair was thoughtfully designed specifically for canoeing. I like the rigid back, the straps to hold it on the canoe seat, the floatation, the ability to lock it closed... all well thought out. I'd like it if the straps were a little shorter so that it could be closed to slightly less than 90deg to provide a more upright support. I might try to make that modification myself. But great chair. Sturdily built.

This is a well made seat and there probably isn't one that's of higher quality. That said, it was useless to me in the rear of a 16' Wenonah Canoe that I took for a week into the Boundary Waters in MN. The taper of the stern meant that the SitBacker could not fit completely on the canoe seat...it was difficult to position it so that I could even get the seat-back in an upright position. Some minor design changes could have accounted for this common issue...not sure why the manufacturer ignored it. A couple other annoyances were to be found. One was the "portage lock" which was a good idea but in practice was poorly implemented. It rarely stayed locked on a long portage. Also, when entering the canoe, there was no good way to keep the seat-back upright while I pushed off from shore and got settled in. Particularly frustrating on days when winds were high and you had to get underway quickly from shore. This thing would work fine in the front of a canoe. It would also make a fine stadium seat. In the end this was a mediocre piece of equipment for my needs that did not perform to my expectations. In other situations it might be great. Just not mine.