With a non-inflatable you would become buoyant inside the aircraft which could make it very difficult to move. ..... Swimming well in the context of aircraft survival means being able to swim underwater, open a door/hatch that is under water and then go through that hatch. Doing that with an inflated PFD or non-inflatable PFD is not a good plan.
Finding a way out is your primary concern, once clear of the aircraft you inflate.
All true, except for one point. I've been to "dunker training" a couple of times and one point they always make very strongly is that if you find yourself swimming freely inside the aircraft you are probably going to die. Escape from a ditched aircraft is not really something one can cover in a short post, but rather requires practice. However, the sequence, at least as I was taught, goes something like this:
1. As soon as you board the aircraft,
before takeoff, look around and plan your exit route. Pick a reference point you can grab firmly (see below). Locate the nearest way out, and memorize how to open it. Plan how to get there from your seat.
2. Keep your harness or seat belt fastened snugly.
3. If you have any warning before the aircraft ditches, try to assume a protective position. Try ot protect your head, face, and limbs.
4. After ditching, the aircraft will probably end up in some unusual orientation (see below). Before the cabin fills with water, take a deep breath. Visibility may be reduced, or it may be totally dark. Don't expect to be able to see anything. If you are lucky, some aircraft may float upright for awhile, but don't assume they will.
5. After the aircraft hits the water,
do not immediately unbuckle your seat belt, but wait a couple of seconds for the aircraft to stabilize. (Helicopters usually roll over upside down, because the weight of the engine is up on top. Single engine fixed wings often turn nose down, because the weight of the engine is in front.)
6.
Grab your fixed reference point before unbuckling your seat belt! 7. Once you have a firm grip on your fixed reference point, then unbuckle your belt, and
make your way hand over hand to the exit. Always have a firm grip on something until you are completely outside the aircraft.
8. Once completely clear of the aircraft, you can inflate your PFD.
The last time I did dunker training they made us do it wearing a regular Type III PFD, just to make it more challenging. The same type PFD one might wear kayaking or water skiing, about 16 lbs floatation. The buoyancy did make it harder inside the aircraft mock up. However, using the hand over hand technique, one could still successfully make an exit. A good confidence booster.
EDIT: Check out
this video. Listen to the Marine's comments. He was lucky in that he found a reference point before he ran out of air!