There is a few threads on the C4 one that is 10 pages long in the gear review section.
What style of riding are you in to?
I've got 2012 C4s which is very similar, and at first I hated them and wished I bought an Edge or something a bit more freeride, but as I'm progressing I'm enjoying it much more.
If you want to just boost and free ride than the Edge is the go.
I bought mine to progress in kiteloops, unhooked, and ride in the surf from time to time. As the old saying goes it's how you use it

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If that's the type of riding you do then they are great. I've also heard some good things about the Blade Trigger. All depends on your style.