I like the idea of a practice capsize, but I'm not sure I'm too worried about having the PDF hanging off the mast after it had saved the boat from a possible turtle. I guess we'd want to think about how to attach it in the first place to minimize any interference it might offer after deployed.
My crews can be inexperienced, perhaps sailing for the first time, so I'm thinking of aids to help avoid big problems. As I say, just an idea I'm mulling over, thanks all for the comments