Had been meaning to get one for ages, finally got around to it this month...
Wish I HAD done it ages ago

what a bloody brilliant thing -- if you don't unhook. So much more comfortable and freer movement! Just a great feeling...
Used it two days now on the rope only, on a Mystic Star waist/seat harness and predominantly on the 2015 Fusion, with my Dialer directional and the twin tips. I still greatly prefer seat harnesses, and while the spreader bar pad still gets gradually pulled upwards, it doesn't rotate and dig in my guts/sternum at all.
Add to that how much freer your hips are, how much more comfy riding is, how much less strain in the back from fighting the torque of the fixed spreader bar... it's the best money I've spent on accessories ever.
On the directional...
After the first few moments of noticing the hook slide, I very quickly forgot about it and just enjoyed riding the board. The easiest way to describe it is: flowing. Not having to fight the fixed spreader bar means my success rates for swapping stance has gone through the roof... even swapping from heel- to toe-side
before the change of tack is dead easy now. I used to manage maybe one in five, with careful planning and much wobbling and sinking, but now I'm making them 9 outa 10 without thinking. General fannying about in "waves" (edge to edge playing; you can't dignify what I do by calling it surfing, or even carving) is so smooth and easy.
On the TT...
Hmm. Took me about an hour of being too lazy to change it to get used to it. Very quickly you get used to not waggling your hips around, as being unable to use the resistance of the hook is a bit weird, and getting pulled from slightly
not the direction you're expecting can be disastrous. Basic tricks are no issue; just make sure your hips AND shoulders are squared up in the right direction for landing. But I got used it eventually, and I doubt I'll be going back to a fixed bar.
Concerns...
Breaking the rope. But if it was made of dental floss, it's still be tougher than a Dakine hook.
Breaking the pulley. See above.
No in-built knife holder. Awaiting the next version pad...
In short -- it rules. Shut up and get one.