Just back from the spot, http://www.kiteboardingcostarica.com/
8/8 days riding, 10.5 m only once, 9 m most of the time, 7 m twice (I'm almost 220 lbs) - and it was not very windy, just a beginning of the season, I was told.
They don't have really flat water, no downwinders, no waves. But endless wind, very nice people running the place, reasonably priced, basic yet clean and practical accommodations, tasty and plentiful dinners for $10, and great snorkeling beach around the corner make it quite an appealing option, and there is plenty to do if it gets too windy, with various side trips, zip lines, diving, hiking, etc.
If you are into huge tricks - beware. All their instructors have stories to tell, and scars to show, the wind has a nasty habit of shutting off when you are in mid-air.