Anyway they're essential the same units internally/precision wise, the only difference is the body style. The 52-2-13 has a straight body and the 52-2-12 is at an angle.
hahaha thanks for bringing this to my attention....a year later
Well clearly this was on oversight in response to Seattle_Aquarist question so I stand corrected
In my defense I did give the right info but for the wrong part #
If you do come across the 52-2-12 or 13 for a cheaper price get it! It will allow easy dialing in of your Co2 with precision. Having the 1/16 orifice is great but is way overkill for our application and this will not let you grow plants any better than the 52-2-12 /1 3 or a Fabco. Honestly, you'd be better off getting a true dual stage regulator over a highend needle valve. Consistency is you need, not a ultra precise needle valve because that will not stop the Co2 fluctuation that occurs due to varied reasons.
If you are getting both then great, you will have no problems and thanks again for bringing this to my attention.