as long as you dont let them backload they will last. i remember reading something from WCR about they are safe to backload upto 8,000 RPM but i wouldnt chance it if its possible to get around it.
just like anything else, when you cut metal you run the chance of weaking its integrity, but thats a risk most are willing to take. at this point these guys cutting them have the bugs figured out. if for any reason yours goes out its almost certain its not because the guys cut it wrong. ( this is assuming you get one from an experianced place)