I had a Sunto M5 (I think) from a few years ago. My wife got it for me in 2005.
It sucks compared to the foretrex. Hard to program, slow, not even close to real time. I am sure it has been redesigned, but go with the foretrex. I hope they have redesigned the strap though so it doesn't fall off so easily.

I like the fortrex because on one screen you can have your speed, VMG, Heading and Bearing. The heading and bearing doesn't come into play for bouy racing though.