To be honest, I bought a "dinan" chip off eBay as well (stupid not to figure out it was just a copy) but it should deliver just the same gains as the actual Dinan chip.
If you can't tell which one its a knockoff of, Mark would definately be able to help you.
On the side of a chip, Mark's is one of the best (especially if you can get good 93 octane gas, as his 93 octane chip for the M42 is supposed to be AWESOME). I would not recommend anyone buying a chip off eBay, I was living in a fools paradise thinking they were actually legit. Albiet they probably work fine and mine has had no problems, you aren't supporting the person or company that spent their time, expertise and hard earned money developing these chips. Intellectual Property should not be devalued just because its easy to copy software

And yes, chipping a M42 from stock will undoubtedly produce more than 5hp or whatever JohnW quoted. BMW still does have a marketing department that wants to make sure there is enough of an incentive to spend the extra money on a 325i, let alone keep tight emissions, etc that get relaxed when doodling with chips. They have to keep enough room performancewise between the models. I think MarkD even provided some input
