I bought it to replace the basic HH pedal that came with my son's entry-level TD-1KV kit (in addition to a KT-9 to replace the kick pedal). I originally considered an upgrade with the cheaper FD-8, but once I realized that it uses the same rubber mechanism than the one I had already, I felt there was no point. I'm not quite sure what mechanism the FD-9 uses, but the difference in playability is massive. It is super quiet, and with great responsiveness. I can play heel up or down without problems. It's extremely robust as well (metal, with solid plastic on top), so I'm sure it will last long.
I removed one of the two lateral springs to make the action slightly softer. Great product!