First I will say - I am not the biggest fan of throttle locks in general. I understand the inherent risk in using them.
I recently went on a road trip that was 5 hours each direction. I have made this trip before and decided I wanted some sort of "cruise control" this time to give my throttle hand a brake. I purchased the Omni Cruise: OMNI-CRUISE: Universal Motorcycle Throttle Lock
For this price this device worked really well for me. For those that don't know - Installation is very simple (60 seconds maybe). A band is placed on the throttle grip and the device is placed over the band and tightened.
Using it was simple as well. Roll the throttle where you want it, slide the omni-cruise in place (rests against the brake lever to prevent the throttle from rolling forward by friction), and you're good. It kept the throttle in place pretty well. Minor adjustments were easy to make.
Releasing the lock was easy - simply roll the throttle forward. It did take a little "getting used to" but the learning curve was short. Just have to keep in mind that it's in place.
I didn't ever really take my hand off the throttle (maybe for a second or two) but it allowed me to relax my hand.