I can't speak to the E46 upgrade of the 325, for a couple of reasons. I order a Conforti shark from Turner Motors (or whatever its name is), actually the service station order it. In fact, I ordered two Conforti sharks one for the 330 and one for the 528, without a long boring story, neither shark worked. Paranoid it was my car, I took the 528 in for a Dinan software upgrade, spent a lot and was paranoid I had wasted my money. I have to say, I was pleasantly surprised. I can't say the car was much more significantly powerful, but I noticed more punch in the lower gears, where I wasn't expecting it. The software not only changed a number of factors affecting the motor and combustion but re-mapping the transmission as well. I think the significant boost at the lower end was from the rejuvenated transmission.
It was unfortunate I had such a negative experience with the Conforti products - I'm convinced something is wrong with them. I would have preferred the Conforti product as you get to keep it. Whereas, the Dinan software upgrade (done at a local BMW dealership) was a one time only deal; if I lose the software for whatever reason, I have to pay again for another reinstall, which I'm not to thrilled about.