Although going to elite FUT specialists such as H&W or Rahal will more likely increases the chance of a satisfactory result in terms of both scar or growth yield, I agree with you that nothing is 100 percent. HT or any cosmetic surgeries itself isn't without risks in nature. If we are being conservative, prepare for the worst, in my opinion, it is the best to go for FUE instead because, in the worst situation, we might end up with a very low or even zero growth yield and a strip scar in the back of the head for the rest of life. On the other hand, FUE is less risky that you will have one less thing(scar) to worry about if the growth yield turns out to be very low.