I really like the Gold Finger left hand throttle kit. I found it very intuitive to use and I use it about 50% of the time while I'm riding. I wish it were about 1 inch longer though so I could put 2 fingers on it. That would make it even more comfortable.
Take your time tapping the hole and watch the threads on the bolt that goes into the hole. My threads on the bolt were a little messed up but thankfully I had a 10-24 die to clean them up. I would also only tap the hole as deep as it is needed to fully seat the bolt and still leave a little play in the throttle connector. That way it can be tightened down all the way. If I were to install another one of these in the future for a buddy, that is how I would do it.