Hi Mal,
I put a Haltec Platinum Sport 2000 in my csi at the end of last year, massive difference in drivability but not a power upgrade as such.
When I bought my car it was still running the factory ecu but problems with the ignition circuit including cutting out and leaving me stranded a couple of times, led me to a specialist BMW shop that advised replacing the ecu with something more efficient would solve these problems. They fitted a Microtech unit that was wrong for my car, a unit with poor adjustment tables and is used generally for rotaries or drag cars, and failed until later to find the ignition problem, a poor connection at the key end of the circuit, the can ran ok but not great. Having taken the car to various specialists for further tuning it became apparent that the ecu itself was the problem and the advice was to replace it with a Haltech. I was lucky enough to have some contacts with company itself and was able to have them supply and fit the unit along with an electronic coil and now the car runs well, starts on the button and generally feels like an 89 3.5. The next mod will be to have the distributor 'locked' so the ecu will look after the advance as well, although I am going to wait and do that with a cam swap at the same time.
All up the swap cost approximately $2500 although I was lucky to be able to use a second hand unit which saved a fair amount.
Recommended.
Cheers. John