It is a good, all metal, classic downstream 2nd. Easy to service, and all of the "annual" service parts can be found from "generic" sources if you cannot obtain the offical Mares service kit.
This reg has a low "parts count", and is easy to service.
Check to see if your local dive shop services Mares regs; otherwise there are shops you can mail the reg to for service (Scubatoys is one).
Having said all that, make sure you are getting a good "deal" (and this applies to all used regs). All of my recent reg purchases were great deals (found on ebay), and I highly recommend buying used if the price is right, if the reg is in decent condition, and if you have done your homework regarding service and parts availability.
Have fun with whatever you decide.
Best wishes.