Has anybody tried these for windsurfing? Any good?
They look nice and simple to use and easy to get data, but hard to tell how big they actually are and if they would be a hassle wearing on arm??

GPS Speed surfing dosn't say much about them apart from they trialling them.

www.velocitek.com/pages/speedpuck

This sentence from the specs tells why they are not suitable at the moment:

Data Logger: Lat, Long, Time, Speed, and Heading recorded every 2 seconds, 20hr capacity. Data download is compatible with Mac OS X and Windows

Not too bad if you aren't worried about 2s average or alphas

They are 115mm diameter and weigh just under 300g. So I don't think an arm mounted solution would work too well. The data logging can be set to 1 second intervals, 2 second (default) and 4 second. I am not sure that the heading and wind shift functions would be of great use windsurfing either. But for dinghy and yacht sailing it is an awesome tool. Cheers.