I have a Go Cruise 2 CNC aluminum throttle lock cruise control. I've read that the Atlas throttle lock is better. Then there is the Break Away throttle lock, and the Vista Cruise throttle locks. And there are also other throttle locks that replace the bar end weights.
I don't know how to size any of those others (other than the Go Cruise) but I'm sure there is one that fits the 7/8" bar on the AK 550. I do know that many of those others will cost more.
There are also true cruise control systems but I have no idea about those other than that they can be a real bear to install and have no info if one can be put on the AK 550. I'm sure it can be done but don't know that the makers of those know how until they get an AK to practice on.
I only use the GC2 for very short spurts on flat level road to shake out my right hand and wrist. I can tighten the knob on it to hold the speed rather well until I come to a hill. Even so, I find I rarely use it even though I do tend to ride at least 150 miles to 180 miles between tank fill ups without stopping and as much as 460 miles in a day. That long day (for me) was on the way back from my last camping trip at the end of September. And I don't remember that I ever used the GC2 on that day at all. But I do find I just have to have my Cramp Buster tab on the throttle grip to make those miles. I can relax the fingers on my right hand and just rest the palm of my hand on the Cramp Buster to hold my speed, even on hills. I will often simply lay my fingers over the top of both grips and over the brake levers to rest them without ever letting go of the grips.