I have two Pro-Dytters mounted on one ear. I cannot imagine not hearing them on a dive.
As for the Pro-Track, I'm not interested in how fast I fell or for how long, I just want to hear something warning me that I should start doing something in the eventuality that I am too focused on the dive and lose altitude awareness.
One of the cool things you can do on a protrack it set it to beep above 6500 feet. I've set mine to beep at me @9000 on a few cross county jumps just so I remember to look at my altitude. The loging function is cool too. reminds me just how many jumps i made each day. It also reminds me that the bank statement is going to say NO MORE!!! Oh well! Any one want to jump?
I bought me a skytronic FX a few months ago. I like having everything done for me, it makes logging jumps easy. It was kinda a pain to figure out how to set it up because they forgot to add some of the instructions with it. I wish you could adjust the volume in it though. It is hard to hear when I put it in a protec, but in a Z1 or other nice helmet it is fine. But I enjoy it very much. And I feel it is much better of a deal than ProTrack, considering it does all the same things.