In a word, excellent. I'm a heavy DIYer - engine swaps, transmission swaps, etc are nothing for me and my friends. But sometimes you tire of spending endless weekends in the shop and want some family time, right? My friend and I built an E39 M5 wagon (touring) and supercharged it, but it wasn't running quite right and needed a tune. Since I was going to have BPC tune it anyway, I decided to ask them to weld in a rear diff mount reinforcement plate and also add water/meth injection before doing the tuning. They found a unique solution for me, got it running, and now it drives like a stock car until you get further into the throttle. Amazing job, excellent customer service, easy parts availability, and friendly staff all around. Everyone there truly cares about the outcome and will spend as much time as you need talking about options and ideas. I've already been back since this visit and will continue to go there whenever I need something. Highly recommended.