I have a 5'9'' s-quad. ( Other gear Best Waroos 9,13,17, Underground FLX 122, 142) I weigh 74kg and have been kiting nearly 5 yrs.
I love this board. Prior to this riding an old 6' glass surf board with straps in the surf. Still use this and a big (17M) kite if the wind is light (10-12K) but the s-quad is great once the wind picks up.
I can use the s-quad in the same wind/kite as my 122 TT.
On flat water it is very smooth and fast. Not as much "rooster tail"as a twin tip but the speed is just as fast and of course it points better.
Turns easily, especially as weight is moved further back. I often ride with the back foot out of the strap.
A bit harder to Gybe than my surfboard but good to have a new challenge! Its easy to lose your carve in the turn while gybing and start heading too far downwind. This cause a loss of power in the kite and soon you're hardly even moving. If power is a bit light I downloop the kite as I enter the gybe and power away. The board just feels great under powered turns.
I'm still getting the hang of surf in mainly 1-2metre waves on Victorias west coast but initial experience has also been great. The board is well balanced and turns easily on a wave. Board can be slowed right down but still under control when going out thru the break or riding a wave. Also jumps in a nicely balanced way making it easy to land, not much different to a TT.
The under surface seems to be easily scratched - haven't tried to polish these out.
Fins don't like rocks/reef (whoops) but seem to be well manufactured and stiff.

In summary a great board to ride but I can't compare it to anything but my SB and TTS.