FI is safe as long as you stay somewhat lower boost. 30k miles is fine, I know a guy who's had a SC on his 350 for close to 80,000 miles with no problems. Just don't redline your motor all day everyday and you're fine
Go with GTM, hands down. The stillen kit sucks the D in a mean way. It doesn't make much power, it's not reliable, the tune is garbage, and there are lots of design flaws. PM Osiris for more details, he has it and he's had to do ALOT of work to it.
I survived Zdayz 2013... (barely)