I had the ACS3 system but didn't like the pneumatic bottom out, HBO is much better.Interestingly the latest FTR email compares the Smashpot to the ACS3, with the Smash coming out on top mainly due to the better bottom out. Backs up the comments i've been reading on the forums also.
Just rode my bike with the 50lb spring in the smashpot and with the travel set to 170mm (up 10mm) and holy moly it is good! I might have to extend the Mezzer too for a fair comparison.