Originally Posted by BC_Dan

Aftermarket reeds allow a bit better airflow over stock. More air = more HP possible. On a stock 500, you won't notice much gain in performance because the stock reeds are not limiting you a whole lot. If you increase airflow to where the reeds are a bottleneck, adding aftermarket helps a bunch. Larger engines with aftermarket pipes and aftermarket intakes show improvement, even more so if the cylinders are ported, because the increased airflow makes the reeds the weak point.

I don't think I would spend the money on a stock 500, there are better improvements you can make for the bucks, such as aftermarket can/pipe combos. If you have already done other mods, it's your call.