So far I am pleased. I think it is pretty expensive. I have more than 1k in it so far, and I plan to use better connectors than the blade connectors supplied to hook up to the powered stuff. But I don't think you can compare it apples to apples to a system like the one that came with my RCR. I don't think there is anything you cannot do with standard stuff, but it is much easier to control things in complicated ways. You run almost no load through switches, so dash reliablility should be improved. It does significantly reduce running wires all over the car, since you just have a couple of wires connecting the boxes.
For example, I have three fuel pumps, and a solenoid valve that selects return flow to side tank that is active. I will have it so the pumps are activated by ignition on, but the EFI system will actually control whether they are powered or not. And a single switch on the dash will decide which of the in-tank pumps is active, and what state the solenoid valve is in. This is easy with the ISIS but would be a stretch for me without it. Plus, if I want, I can have the ignition as a button on a key fob, with no key. And the EFI wire goes straight to the mastercell about three feet away, but no additional connections are needed back to the fuel pumps, as the CAN bus does the controlling.
I'll keep you updated as I go along. I am getting ready to have ISIS reprogram the mastercell, so I'll let you know if that goes smoothly.
-J.