I have a Ronstan Clearstart RF4031. There are (I think) 4 watches in this series. I read the manuals for each one, and I don't see any functional difference. The only exception would be the huge one, which is probably best mounted somewhere, as others have said. Other than that, I think the differences are what the band and/or case is made from. Mine is the cheapest at about $50.
I think this is a better tool than a regular timer, mostly because it has a sync button. This button allows you to sync the countdown with the race committee. So if you miss the first gun by a few seconds, you can sync it a minute later.
It also knows the 5,4 1, GO sequence, and makes all the different sounds at various times. But, I don't think its loud enough. I would like it to be MUCH louder.
Its also nice that it will start counting up after it hits zero int he count down, but it will only count up to an hour. So if the race is less than an hour, its useful. I'm not sure if it will wrap around to 0 as it counts up past the hour.
So, in my club race I am in class B, we're the second start in a 5,4,1, GO sequence. I can set it to count down from 10 minutes and then to start counting up.
As for the skipper not keeping the time himself, probably a good move. I dedicate a time keeper for this task. As for not knowing when the starting gun is going to fire (or the shape dropped - the real signal) well you just can't have that.