It's a valve with a toggle on it. When you pull the line it opens the valve and it inflates. The only thing that can go wrong is if the valve gets somehow rusty and locks up (unless it's some kind of self-inflating mechanism).

The stress on using the bottle is not good as you stated. The bigger problem is getting the bottle refilled. I don't think anyone will do it if they think you're certifying it yourself.

It's not difficult putting it back in the valise or case when you don't put the extra stuff in. Better not to put it in and have a ditch bag as you can put a lot more stuff in the ditch bag and you need one anyway. (vhf, epirb, water, Snickers, water, money, passports, Solas flares, smoke flares, water, fishing gear and a lot of other crap.)

Chances are you won't need much stuff if you have an epirb that's currently registered.

In most cases your dingy is a better liferaft anyway. If I hit a container, I'd rather be in the dingy with a full tank of fuel and an epirb then in a liferaft without an epirb.

The first Avon I self certified was rotten. I manually inflated it and it fell apart. Had a big rotten area of the material that you could punch your finger through.