My Bon 4 just arrived! I seem to have a pretty good fit already, which is promising. It's comfortable enough that I'm going to try sleeping with it on. Wish me luck!
S So far, so good! There was a little pinching when I woke up but it has been remarkably comfortable. I'm aiming for 24 hours for the first trial, then assess from there. I have the key with me just in case, right now I'm experimenting before making the formal request to my (hopeful) keybolder.