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The Greddy E-manage is well, I guess the best term would be "super piggyback"... It's much like the MAFT-Pro, MAFT Gen II and MAP ECU. With all of these the stock ECU remains in place and these devices intercept and modify sensor and ECU signals such as air flow (used to control fueling, there are set backs to controlling fuel this way), ignition timing (can be used to correct for the aforementioned problem), boost control, air flow meter conversion and so on. You can get all of this with a couple separate devices or got with one of the "super piggybacks" and get it all in one shot. On upside to getting a device with everything rolled into one is the ability to record what everything is doing on your laptop where you might otherwise only be able to log one device at a time and have to learn and use a number of applications. On the down side having to learn all of this at once can be confusing for many people and often ends up in abandoned projects. I don't recommend them for the novice unless it's not their primary vehicle or they can otherwise afford some likely downtime.