Although experiences vary, you really need to be on top of DIY or have a more intricate setup that I did. The problem with CO2 is that unbalanced amounts can potentially wreck your tank by letting algae bloom. It's less likely in a low light tank but certainly not impossible.
On top of that, DIY is a pain. Injected is literally set it and forget it. I did both and I wouldn't go DIY again. Having said that, I'm not sure if I wouldn't have given DIY a chance to begin with if I had to do it all over again because I did learn a lot. On the other hand, it was a 5 gallon, not a 55G.
The only caveat to pressurized CO2 is money and if that's the thing holding you back, I would go DIY but continue to save up for pressurized. I say that because I really think once you go down the DIY path, it's only a matter of time before you'll be injecting pressurized. In fact I don't know anyone personally that remained with DIY for a more than a year - most no more than 6 months.