Use whatever tools you need to have a good performance! If you use a prompter you just need to get good at using it; great public speakers give amazing speeches that sound from the heart and spontaneous even though they are on a prompter!
Yes J x 3. I just learned that Bruce Springsteen uses one! Edited to add: to us it all looks very sponateous if someone calls out a song and he actually plays it! I read that he expects the E street band to know it ( after all they have spent years playing the pubs) but he has a very nifty tele prompt operator who quickly brings up the lyrics.