The reason I switched to grip shifts is I have arthritis in my thumbs and triggers (at least the old Rapidfires) hurt like hell. I switched many many years ago--'have a early set on my Stumpy; 7-speed and they were actually "Grip Shift" brand then. And before the "old man" comments start, I was 29 when the arthritis showed up
'Never had an accidental shifting problem (that I can recall) on the Stumpy with the old Grip Shifts. On my new bike that has X.9s, I have accidentally shifted a few times though..usually when I was floundering\struggling on a hill/tech section. Forward motion would've soon stopped anyway...
I tend to ride with my index finger and/or middle finger on the brake levers (left over from the ol' motocross days I guess), so I'm conditioned to hang on to the grips tighter with my outer three fingers on each hand. This might be why I haven't had any real problems with accidental shifting using the grip shifts :hmmm:
Tim