I don't like piggy backs because at the end of the day your just riding a stock ECU. I've found with piggy backs that the AFRs can change over time, and same with the ignition timing because the stock ECU plays with them and theres nothing you can do with it. What about when you do an ECU reset, your fuel/ignition maps are not right anymore because the ECU is starting to learn its fuel/ignition correction tables from scratch again. Chuck on bigger injectors/AFMs etc and you can just imagine how hard a piggy back is trying to fool the stock ECU. You can only do so much!
Stand alone you have complete control. emanages are for tightasses who cant go the extra mile and do it right with a PowerFC. All the talk about A/C and cold start etc is a completely non issue with PowerFCs. Hell it even has closed loop when tuned good. What more could you ask for, for the price? PowerFCs are so cheap now. Back in the day when they were closer to 2k then its understandable. Remember $500 difference at the end of the day when you add up the money you waste on modifying, is not much really.