A lot of ECU's use simplistic TC systems rely on simply fixing the rpm at a temporary limit which is lower than normal - they take no account of what is actually happening between the tyre and road and the grip afforded by the road surface.

Better quality ECU/TC systems have multiple wheel speed sensors which can sense whats happening and act accordingly.

I've used TC systems from both Motec and RaceLogic both of which do the job very well. Racelogic being more more configurable (unless you have a Mx000 range ECU...)

It just so happens I've got a RaceLogic pro (with 12 position adjuster) for sale, includes 4 wheel speed sensors and spark cut interface. It is NOT suitable for hooking into vehicles with ABS and fuel injection. It IS suitable for something with a dizzy and single coil eg RWD Pinto / BDA etc