Plenty of cool TDIs available and friendly, honest mechanics, but that's just about where the positives end...
My parents test drove a TDI Jetta wagon that was in reasonably good shape, albeit priced quite high. Although Ali was extremely knowledgable and friendly, my parents were subjected to a bit of pressure from the salesperson they talked with. I drove over to test it later and found the saleswoman to have little personality or interest in me as a customer.
I returned to test a TDI Passat wagon in rough shape that was still fairly overpriced. The drive went well, but there was no salesperson to help me when I arrived. Props to mechanic Valentin for helping me out even though it wasn't his job!
Finally, I called the dealer on a Friday to drive another TDI Passat wagon, and was advised to call on Monday while they were completing a fuel door replacement. I called Monday morning to find that the car had been sold on Saturday. I wasn't contacted or made aware of the fact that the car could have been sold during my waiting period. There are benefits and downsides to their online ordering system...
Based on my experience, if you talk money early on or if you're a long-time customer, they'll listen to you and care about you. Otherwise, you'll be dealing with uninterested salespeople and some high prices in order to get what you want.