PMS is a great tuning device, and with teh standalone mode is "almost" an aftermarket engine management system. Its relitivly easy to use anddoes as advertised, but I find the huge drawbacks are no datalogging wthout the expensive interaq software, and no AFR read out on screen unless you buy the anderson wideband. I think its great for dyno tuning in a controled environment with the right equipment and can solve a lot of issues, but its no where near the spec and scope of an AEM EMS which allows total control and has a million more features. It does away with the maf (though you can use it to tune with a maf if you prefer) in favor of speed density, which is easier and ffar more accurate, especially for bboosted applications. You have a faster processor and finer grain control, and can litterally do anything you want with it. The learning curve is steeper, but its got great support, and best of all you can tune on the street with it (I have) with relitive ease.