Use whatever you like, thumbs, fingers, whole fist. It doesn't matter. Heard all the arguments of one over the other... all are total bunk. Similar to the radio tray or no tray argument. It is totally personal preference. Tell Chip Hyde he's not an advanced pilot (he flys thumbs.) Many others at that caliber also fly thumbs... then again, many also fly pinch. You will find a lot of strong personal preferences from pilot to pilot, and reasons why they fly a certain way or a reason why they switched. In the end, it all comes back to what you like, no need to justify it any more than that.