I have the Plug-in Pro on my R32 Skyline GT-R (1000cc injectors, big cams, T72, twin tial 44's, 90mm throttle).
It is a phenomenal system. Software selectable high/low imp injector drivers, sequential injection, direct ignition not waste spark, 3 methods of tuning (Lambda, direct, and VE), usb connection, all kinds of correction tables, boost control, on board map sensor, etc, etc.
The software is rather easy to use. It only took me a about a day of fumbling around to figure it out, and once you have the basic concept down, it is very user friendly. I was rom tuning the stock ecu but it is just too slow to keep up, and the big throttle was a big problem. The Haltech transient throttle tables are just sooooooo nice. I can pump the throttle any way I want and the A/F's stay rock solid.
Crispeed's praise for this system and the results he's had on his customer's cars is the main reason why I bought it. I am 110% satisfied with it.