Garmin watches are ok and from using them in the past for running they are really accurate at tracking distance and speed, but for kiting they are useless at measuring altitude for jumps. Borrowed my girlfriends Forerunner 205 2 weeks ago and pulled the data into the Garmin Connect website. Speed and distance is accurate, but I never really got over about 10m and definitely don't think I hit 20m!
Only thing is if you do look at one for using for kiting, make sure it is waterproof as most of them aren't. Hers turned out to be one of them that isn't and started to fog up inside after a couple of 5 - 10s dunks due to some high speed crashes.