ridden both, in the end I bought the smashpot.
Borrowed a friends Factory 36 Fit4 29er with the ACS3, which was very good, the air element was super sensitive to pressure changes. The difference of a few psi went from no bottom out control to feeling like it had 10 tokens in it, this may have been install issue or whatever I am not sure, However the initial stroke was plush and the mid stroke was controlled which is all you can ask for.
I guy locally was selling a smashpot 1 ride old for near half price of a new kit... with the spring that was reccomended for my weight and travel (170mm on 29er) so I rolled the dice.
Chucked it into my Fit-Grip 36 Rhythm in about 20 minutes (so easy) slowed down the rebound 3 clicks from my usual air setting and was in Fork Nirvana! It reminded me of my old Coil Fox 40 in a way, but the bottom out control is absolutely seamless and controlled. It's dead silent too.
Only con, yes it does add some weight. As soon as you ride it, you don't notice it at all.
I don't think you will regret either, speaking to my local suspension guru's they were very positive about the vorsprung kit (they sell both brands)