I ve taken hillclimbers out for rides. the stock length bikes can dodge and weave alot better and absorb the bumps, especially on down hills better. extensions really just slow down the abrupt wheelies on the hill. ( So you can stay in it WFO) Extensions also change the traction so you will have to search for the right gearing/tire combo. They also really affect the spring and setting of the rear shock, like Roost daddy said. It took more than a couple clicks to compensate for the leverage on mine. The extensions that we get are polished Aluminum, so we try not to beat up the bling there also. Plus you have alot of other details to work out. Extensions require, buying a new chain or two,( longer than OEM), relocating the chain guide, relocating the brake stay, often a custom brake line and losing your factory adjustment marks.
Approximately 500.00 (not including shock revalve) to add length by the time you get it done. If you do that, get your District Card and Ama card, and put a Tether Kill Switch on it, and Bammo, you're a hillclimber....