I had a BrakeAway throttle lock that was mounted on one of my old VTX 1800s when I purchased the bike. Tried it two or three times and determined very quickly that it was a worthless and, yes, very dangerous, $180 POS and never, ever used it again.
The clip-on Throttle Rocker/Crampbuster is OK for folks with nerve or muscle problems in their right hands or as a cheap and easy way to rest your left hand, but I'm a big believer of always having your hands on or at the grips/controls and at the ready 100% of the time, so I wouldn't bother with them either.