I stick with known manufacturers chips. Many of the ebay chips are copies of these chips, and likely fine, but it's essentially stolen. I would rather support a company to inspire them to continue to offer products for bimmers so I can keep putting go-fast parts on my cars.
Watch that your high octane fuel does not have ethanol added. Best I can get (non race) by me is 91 no eth. The 93 has 10% ethanol, and the car runs MUCH better on the pure 91. There is a station about 10 miles from my work that has 106 on a regular pump...