When I had Dudley (my first NT) I had started with a Throttlemeister throttle lock. In my opinion, it did a better job as a cruise semi-control on the NT than anything similar had done on my Kawasaki Concours. I decided that might have had something to do with the nature of the torque curve on the NT. It seemed like the NT did a better job of holding speed in rolling terrain than the throttle lock I'd had on the Connie did in the same terrain.
But, throttle locks don't even begin to compare with a real cruise control. I had a Rostra cruise control on Dudley, and I've got an McCruise control from Australia on Horse (my 2nd and current NT). Because anything I do (pulling clutch, touching a brake) disconnects the cruise control, I end up using it a whole lot more than I did the throttle locks. I highly recommend the cruise control if you're riding longer miles.