Doesn't a CB550 have a throttle lock from the factory?
I'm not sure, the early CB750's had them, but they were phased out after around 1973, from memory. Probably not a real good idea to use one as a cruise control (although I have once or twice) as you can't release it as quickly as you can a cruise control.
That's where the "Brakeaway" system is great, tap your front brake and it's released, much like the proper cruise control systems in modern cars. Tap the brake pedal, and the cruise control doesn't exacerbate the situation.
The cheaper versions work fine for locking and unlocking the throttle, but in a "panic" situation, the average rider is too busy hitting the brakes and looking for a manageable line thru whatever the situation is to necessarily think to flick off the throttle lock.
I've never tried the "Crampbuster" gadgets, so I wouldn't know of their effectiveness, but the thing that puts me off them (apart from their looks) is the fact that I still have to keep my hand on the bar to use them, so if I do get the "Pins and Needles", I can't take my hand off the throttle to shake 'em out. Cheers, Terry.