I use to think it wasnt really a big deal to have one... Until i really started USING it... Its a great tool and i feel its insane not to use it... Not using it is like if you had an open notebook test.. and you just decided nahhhh ill just go off what i can remember
Once you use one it's so hard to go back to not using one. I honestly cannot imagine playing without mine now. I'm only playing at micros so am just using the basic stats like vpip/pfr/3bet etc rather than some of the more complex stats but no doubt in time I'll be using them too. You'll make the money you spend on a HUD back in no time.
If you play on Carbon, their own HUD is a licensed copy of Hold'em Indicator which is a very limited (by comparison to PT/HM) but functional free HUD. Other than that, you really just need to buy PT or HM.
A lot of fiddling actually. fpdb has been around for years but has never really been very usable. Unlike a lot of open-source software, it's nowhere near as functional and stable as it's commercial competitors. And I say that as a decades-long user, supporter, and contributor to OSS.
Since there is such a significant likelihood that a properly used tracker will increase your earnings, there's no reason not to spend what is really a pittance for PT or HM.