Hey Mike...
For looks you can root in order to theme, install apps such as replacement home launchers, flash a custom recovery to flash roms, kernels, and other files and things of the sort, all depending on the outcome you're trying to achieve.
As far as flashing roms and kernels, they can be stable on one phone but not stable on another of the same model. I've went through it personally or I wouldn't believe it myself.
Also, I've been with Metro for a while and have used so many different phones it's not even funny. As long as the phone is factory unlocked -aka- unlocked bootloader or not tied to a carrier from the factory such as a Nexus, and will take a Metro SIM card, that's all that should matter. I call customer svc and they switch my phones for me for free all the time. You can find used phones cheap at places that fix phones, those little booths/kiosks in the middle of malls, pawn shops... I found a Huawei Premia for $30 mint condition and got it on a trade for an old iphone 3 or 4 I had sitting around and the Premia is still going for $90-$100 used! Just gotta hunt a bit!