I haven't used one yet, but I have one on order to use with my Garmin 310XT for race training.
There's been some discussion of this device at http://www.surfski.info/forum/advsearch.html?q=vaaka&exactname=1&childforums=1 .
Bent Shaft Canoe Paddles
Canoe/Kayak Storage Racks
PFD's (Life Jackets)
Gedi Convertible Helmet