if you feel a pony is the way for you then go for it! If you are diving with unknown, or unreliable, buddies and feel the need for an gas independent gas reserve then it is ideal. For the two dive boat days a single tank and pony gives more gas than twin 12s, provides more consistent weighting and weighs less. It is a simpler and cheaper transition than a twinset and requires little new equipment and no significant training (other than being comfortable switching regulators).
I bought a pony in 2006 and it served me well for a number of years, until gas planning indicated more gas for a single dive than my 15litre will hold. At that point I bought a twinset and lots of other expensive stuff. I still have my single tank and pony setup (it is not for sale) and sold all the twinset stuff and now see that as an expensive dead end I could have avoided.
I back-mounted my pony, with a Metalsub bracket on the cam-band offering quick release, had the regulator necklaced with the hose over my right shoulder, and had the SPG on the right side, opposite to that of my main cylinder. Some folk complain a pony is unbalanced but I found shifting a couple of kg to the left of the weight belt fixed that. It was always turned although I could (just) reach the valve to turn it on by pushing up the bottom of my cylinder.