I use this pedal for six years now and I am very satisfied with it. Pedal is really light and fast, but with some tweaking you can still use it for rock music or for pop. Drive schaft in my opinion is the best feature on this product, slave pedal feels the same as the main pedal. I was using this pedals on double bass drum set as two single pedals but now I am using them as a double pedal on set with one bass drum and i didn't notice any diference in slave pedal.
You only need to be careful with the screws, you can damage them pretty easy with the key that comes with the pedals.
Springs are very durable I broke one after more than 5 years of use.
Pedals are very solid, I added some velcro that comes with the pedal on the plate of the pedal and pedals doesn't move at all. Even slave pedal sits on its position perfectly.
The only con is that I can notice some clicking in the pedals, but after so many years of use, I guess I can live with that.