My understanding is that it's normal to have to top-off inflatable vests once in a while using the manual inflation tube if you're in the water for quite a long time.
The other down-side I've read about inflatables is that they are so bouyant, it can be harder to swim in them than a non-inflatable. But you shouldn't be doing too much swimming while you're waiting for someone to home in on your EPIRB signal (you did leave the boat with one of those, right?). Swimming accelerates heat loss leaving you more voulnerable to the second biggest cause of marine deaths - hypothermia.
For us paranoid types, the other thing I really like about the Spinlock vest is the built in harness without those really heavy D-rings. Add the harness strap - and you've reduced another really big risk factor - you're more likely to stay on the boat in the first place!
Jeesh, its exhausting being paranoid