I've been using an Omni cruise for 2 years. Its OK, nicely made but it does slip. I haven't yet been able to find a "happy" tension for it. If you make it too tight the throttle return spring cant fight it so the throttle doesnt snap closed when you let it go, and if its not tight enough it slowly,(sometimes quickly) loses the setting. It is useful in relieving hand cramp by helping you hold the throttle where you want it with little effort but you cant take your hand off the throttle for very long.. certainly not for a mile.
I must admit I haven't tried using it without the rubber ring they supply that slips on the grip to allow you to close the throttle in an emergency when the thing is set. Perhaps the unit rubbing directly on the grip will give it enough "stick" to work while still allowing you to back off the throttle while its set.