I've used both a Cramp buster and a throttle lock similar to this go cruise in the link below;
Go Cruise Throttle Control Device For 7/8" Bars - TwistedThrottle.ca
Here is the Crampbuster;
There are more expensive ones out there for sure, but if you want an inexpensive one to try, then these two represent your choices.
I started with the Crampbuster, and I really liked it, but found it a bit awkward to use. You see, they call it an "assist" because it does nothing if you let go of the hand-grip. What it does do is allow you to stop GRIPPING the throttle to keep it open. instead you rest your palm on it to keep the throttle open.
Worked fine for that, but I found that it was difficult to adjust "on the fly" as it wasn't simple to twist it in relation to the hand-grip to adjust for varying rates of travel, so there was a lot of monkeying around with it.
Then I found the Go-Cruise type throttle lock.
These grip the throttle and the the extended arm rests on your brake handle, keeping the throttle open when you let go of the throttle. It's kept open by friction, just enough to slow or stop the throttle from closing on it's own. In most cases, it will slowly slip over time, but it resists closing of the throttle all the time it's engaged and even after you let go, unlike the Crampbuster.
The advantage is you can let go completely, wave your hand around in the air, rest it on your thigh or tank, or wave at people...the throttle stays open. Really, really handy on a long stretch of road where you are travelling at a steady speed. It's also easy, once you practice with it to slip a finger over the "arm" that's resting on the brake handle and adjust your speed with a gentle turn of the throttle either way. I was never able to do that with the Cramp-buster.
Disadvantage.....it's a LOCK. A gentle friction based lock, but if you are clipping along on your bike and decide to shift gears, you have to remember to manually CLOSE the throttle during your shift or you will get a sudden increase in RPM as you engage the clutch. Again, once you are used to it it becomes second nature. With the Crampbuster, once you take your palm or hand off the throttle you decelerate, just like you are used to.
In the end I prefer the throttle lock for it's price point, it's ease of use and the comfort it provides on longer rides. Sure feels nice to take my hand off the throttle on long stretches and wiggle my fingers around.