Well currently I'm taking a hit/risk for the cause...lol
One of my riding buddies now has the 16 (and my brother as well) and the 18 is on it's way to a very worthy rider somewhere else in the world as we speak. So in three weeks (being a light 73kg rider) I'm getting the 18m rebel...hope I haven't fucked up!
Anyhow, Toby has already covered this and as usual he's pretty spot on.
The 18 is almost like 2.5 sizes bigger in that is develops a truck of apparent wind coupled with that static grunt we enjoy on this kite. It's so damn stable it's stupid.
The 18 has a lot more hangtime once you effectively convert this into vertical as possible hangtime.
It is also the right speed...the 16 is pretty damn good for the basic stuff, but once you go beyond this, it can fly too fast even on the inner bar settings...can redirect it too fast..technique can sort this though to a degree.
But I wouldn't be passing up a 16 if you could get one. It's still a damn good airstyle kite, second best behind the 18m...lol!!
What I'm saying is we aren't all going to take it to Toby's level are we. For 99 percent of us the 16 is just fine. My bro and my mate have a ball. And me too, if I sit on the beach for long enough staring out like a lost puppy they invariably come in and give me a crack....might be me standing on the beach randomly adjusting my harness without my own kite that could be the hint...bahahahha
Hope it helps...for general airstyle it's real good. And yeh the depowering thing is weird on the 16 ...harder for some reason to control your speed when really lit, but hey it's a matter of grabbing what ya can at the moment...and you won't be dissapointed. I suppose the 16 is better for more aggressive powered airstyle...don't try and do to much or you may find yourself heading one way and the kite the other as you redirect to fast....lol. Speaking from experience.