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I have a shifter kit. It is a very good product. However, you might need to change your bottom brackets. It requires 127mm or longer bottom brackets. You might also find some difficulty in aligning the chain lines. Also, be careful not to loose the key locks, it can slip out if you don't locktite it. I lost one of mine. You also need to paint it, so roughen the surfaces first, use a primer then paint it over with the final finishing paint. Use a heavy duty BMX chain.
You should also have an adequate space between your rear wheel and your seatpost, or install a smaller rear wheel if you have disc brakes.
Before, my Motorized bicycle maxed out 25mph, now it can reach to 44mph in 6th gear.
Engine does not have power anymore after 6th gear. I'm using an 8 speed internal gear hub.There is substantial improvement in hill climbing ability.
Also, Paul is very nice and they give all the support to meet their customers' needs.