shift kit question

A shift kit moves the chain drive to the right side of your bicycle and drives a freewheel attached to your pedals, and therefor transmits power to your rear casette or freewheel and back through the deraileur.

This means that you can have access to a full range of gear ratios instead of one fixed ratio. You have to pedal to start instead of roll starting, and you will most likely need upgraded components (Deraileur, sprocket cluster, chain, rear axle) so you don't tear your rear wheel off.

Long story way short: Lots of tech, cash, and tweaking in, Wheelie power AND face melting top speed out.
Be forewarned though, I consider myself an advanced tuner at this juncture and I don't feel ready to tackle a shifter kit install yet. Too many variables, and my bike is old. Probably needs a whole new rear end. I'll wait till nice stuff starts showing up on the salvage pile.

Shift kits are great but initially require quite a bit tweaking to get the chain tension and alignment just right. I had issues with chain stretch that required almost constant adjustment and improved the issue by buying a high quality Sram chain which only required 2 adjustments and hasn't stretched anymore since I did this. I also had a lot of issues with bearings loosening up on the bottom bracket due to vibration. Just the smallest amount of slop in the bottom bracket caused the chain to randomly jump off the drive sprocket. I solved this issue by buying a sealed bearing bottome bearing cartridge.

Make sure you spend the money and buy a quality derailleur and shift cable....Your derailleur must be perfect in shifting or it could cause issues for you under power.