More accurately its Super Air Flow Convertor II, it's the second generation of intercepting devices that work together with the AFM (Air Flow meter) to basically fool the stock ECU at certain points in the rev range how much air is actually passing through it. If the ECU sees less air it puts in less fuel obviously.
Hence the tuning advantage of such devices, not a substitute for a full ECU but certianly can bring substantial power increases.
And no, it does not have a fuel cut defender, which are evil devices in my opinion anyway.
Hope that helps,