I dont know about causing headaches and what not.
But the tune will never be perfect and you wont be able to fix your flat spot problems or whatnot.
I mean, if you cant afford a proper ecu, then safc would be worth it for what it is.
Uni-group (if you live in sydney), actually told me you will find good gains with it on an r33. Other cars not worth it.
I might purchase the apexi neo sometime soon, and get it tuned and see what it can do.
Fair few actually have the safc in there cars.
50/50 i guess.. some ppl say not worth it.. some ppl will say get it