I've always been picky about this...... I will never let one of my long time riding buddies ride any of my bikes. He is a safe/great rider, but prone to drops, especially if nervous. Many of the guys I ride with now (with a few exceptions) I will readily switch off if we have something different or want to compare, but it happens rarely. Used to switch off all the time when I was younger.
Usually when offered on a completely new platform (modern Yamaha, Ducati, Moto Morini, Indian) I will say NO because I want to remain happy in my ignorance and don't need any more temptation than I already have
