+1. I have Dinan Stage II in my Z4 and had it in an earlier E93. Easy to live with around town, gas mileage same or better, absolute rocket ship at WOT and up on the turbos. Dinan's warranty is great and his limited number of dealers keeps the quality high.
Check for discounts - often 20%. Be careful to keep your dealer from reflashing the ECU when doing other maintenance (though your Dinan dealer will reflash back to the Dinan configuration for free).
