the Z31 swap comes with it's own set of problems just do a search and you'll find all the info (good and bad), I only know one person running the e-manage, and yes it is in fact a piggyback, and they are having problems with it, and yes the greddy will limit your options, if your comfortable building a tuning your own car MSnS is an excellent choice, if you'd rather pay someone else to build and tune your car go greddy