A couple things seem a little bit vague in the BMS advertisement. The claimed power gain (Is it rear wheel or crankshaft?) is 8 to 10 hp. The Dynojet (Known to be an optimistic device) shows 4 to 6 rwhp. If it is 6 hp gain & 2 wheel drive, the drivetrain loss factor could be 15%, this gives 7 hp at the crank. Not sure if the butt dyno is going to notice this in a very heavy car.
For comparison, a GIAC reflash on my 997 S, after already having headers, catalytics, mufflers & airbox, was tested on a Mustang dyno to be 7 rwhp. The testing was done carefully, huge fans blowing into the radiators and the instrumentation reset for each of the runs (3 each, with/without reflash) Definitely felt the difference driving it afterwards, but on a car almost 1000 pounds lighter. Also, 4 times the price of the BMS programming. Altogether, out of pocket around $6500 for probably 25 rwhp. With similar enhancements(and costs), if they could be found for an X3, similar improvements could be expected.
Highly tuned, normally aspirated engines are not going to show significant power gains with just reprogramming. Variability between individual cars may be greater than the claimed improvements and the dyno testing itself is not precise nor repeatable.
2008 BMW X3
2006 Porsche 997 2S Cabrio