I do not belive I have EVER read here a post from someone who was flash tuned
who had their BMW warranty voided.
I HAVE read here many with piggy tunes who have had their warranty voided. (because either the dealer found the piggy box or found the tell-tale evidence of broken tabs, wires, dirty covers moved around under the hood).
Which is safer?
PS: I think the only way BMW could ever tell you have a flash tune would be to download your flash tune and to read the line code line by line. AND only an engineer from BMW AG could do that. I think that chance is fairly rare at the dealership level. Only IF your car was being scrutinized by BMW NA or AG would they be able to tell - MAYBE.