I suppose because where else can you get an around $20 quad or FC that allows for fully adjustable PID's
As far as I am concerned it's a no brainer.
This FC can be put into virtually any frame you like and as long as you can set up the PID's for it and build any other custom circuitry required (typically power distribution for brushless builds), you are good to go. Ian444 on RCG has even done several successful brushless builds using the H8 FC.
I bought the H8 to learn acro too but I have been busy doing other projects so my progress has halted
I believe that for a stock frame the stock PID's in the firmware are pretty optimal from all accounts and from the videos I have seen of people doing flips etc I have no reason to doubt this to be true.
Good luck in your quest to flip