I am of the opinion that a vertical reg is always better than an expansion chamber even with co2, for a few reasons. One, an anti syphon is supposed to draw only gas anyway, so there is nothing after it to expand. Be sure to have your gun always pointed forward or up, never down or sideways, or you'll drain liquid into your gun no matter what you have in front of the tank. Secondly an ex chamber is useless when you do upgrade to air/nitro (and believe me, you'll want to do so very soon) and on any gun you're likely to advance to in the future, whereas a vert reg is useful on nearly all of them. Thirdly, a vert reg has a higher resale value and/or additive value to your gun should you sell it with your old gun or separately. Fourth, the reg itself allows for velocity adjustment.
PMI Pure Energy and Palmer Stabilizers both work well with co2, the PE being very affordable to boot. In short, an expansion chamber is a waste of time and money.