We had one of these strapped to each side of the boom for the entire Tybee. Like everything else on the boat, we taped the snot out of it each day so that it wouldn't go anywhere. After we dismasted on the final day, I took one of them off the boom and put it on my wrist for the final 11 miles, and found it great to have, but annoying when on my wrist as each time I had to lift something or pull a line it would start to come loose. I would highly recommend these units, but attaching them to the boat somehow is ideal.
FYI, We used one last year that Tripp bought new and it got a little water in it, stopped working and we were SOL. This year we each picked one up on EBAY that was a referb model, got great prices, and they worked spectacular even with the stress we put them under.
Chris