The ERL MF2 is an additional fuel injector driver very similar to HKS AIC or Greddy's Rebic 3 units. The MF2 can handle a maximum of 4 fuel injectors but with caution or you'll burn the unit. I advised you use only 2 fuel injectors with the unit.

By using an additional fuel injector driver/controller, its an alternative to replacing your factory fuel injectors for larger ones. When you do replace your factory fuel injectors you'll need to upgrade you ECM or purchase an Apexi VAFC or replace it completely.

There is no difference in tuning a car with an ERL compared to a car with a larger fuel injectors. Fuel entering the combustion camber is the same as fuel entering the combustion camber using 6 fuel injectors on a 4 cylinder car. To properly tune an engine you'll need to know what is happening inside your engine. You'll need gauges like air/fuel ratio gauge and a pyrometer (a.k.a EGT gauge). And upgrade your ECM for an aftermarket like AEM's EMS or Accell DFI or motec or anything that actual has a "real time" data streaming/logging.

The benefits behind an additional fuel injector computer is for the ease of upgradability. If for some reason you upgraded all of your factory 4 cylinder fuel injectors to larger ones and decides that you what to increase the boost, then you'll need to purchase a set of new fuel injectors. With an additional fuel injector controller, you'll only need to upgrade two injectors rather than four. Another benefit with ERL's MF2, you can use it as a water injection (but you'll to buy the water pump kit though). By injecting atomized water into the combustion camber you can run more boost because it'll act as an octane and it'll also retard your timing during high boost pressure.