Thanks for testing the scripts!
I have also on occasion gotten the sinking through the bottom of the plane. The only conclusions I have come to is that the computer has a hard time running the script. In other words its not fast enough to handle keeping the plane in the setpos loop. As it is, I have to run this on my brother's computer to get it to work because on mine I fall through the floor like you described.
As for the parachute opening, the hint can be taken out if you dig throught the scripts a little. I put it there as a recommendation, your right you can survive an opening at a much lower height.
I agree the plane not moving is a downside however you could have it fly for awhile and then go into the call the scripts as opposed to calling them in the init.sqs, just a thought.
NOTE: The plane tends to very jumpy over water. Not sure why, but I recommend using the scripts only over land. Try it and you will see what I mean. Some spots on the map are just better than others.