In response to Arno13 questions:
-I weigh 80kg and i was sailing the wood version.
-I've never sailed with an adjustable mast track so i can't comment.
-In stronger winds (say above 10knots) you definitely have a lot of lift from the fin. i suspect that a retractable dagger board would be less efficient in the light winds the board is really designed for. Also, if you retract the dagger board, the serenity would have no fin whatsoever! On balance i think it's best the way it is. It has a pretty good wind range as it is.
-It could probably handle 15knots but it would be a handful as there are no footstraps. I have no idea what it would be like in any sort of waves though. I have only tried it on a reservoir.
-I don't have a gps so can't help there.
This board is a lot of fun in conditions you don't normally have fun in.