Any top doc will give you a scar that's practically invisible unless somebody analyses your head up close. Dr. Feller who does a lot of FUE puts the number at 75%, if I'm not mistaken. In any case, the failure rate is unacceptably high in my opinion and what you do get in terms of grafts isn't as strong and healthy. In my judgement, FUE is crap.
CORRECTION: the 75% doesn't come from Dr. Feller.