You don't necessarily need to upgrade injectors, although that is the best option. You can just get an adjustable fuel pressure reg and up the fuel pressure a bit to get the same effect, which is cheaper. I love my Profec E01, it's a very nice bit of kit, and it's nice to be able to monitor what's going on in the car without having to hook a laptop up. It was a simple choice for me because I don't have a laptop! When I finally get round to sorting my wideband out I will be able to monitor in realtime and log 3 hours worth of air/fuel ratio, boost, exhaust gas temp (I have a Greddy EGT gauge), revs, speed, injector duty cycle and throttle%. Great if you like gadgets!
As Jake said, the car certainly feels faster because you basically get max boost from the moment the 2nd turbo comes online rather than having it build up gradually to max.
The screen is pretty big and hard to find a place for. I have mine on a mount that's designed for a mobile phone, it sticks out to the left of the fan speed dial.