Regarding the topic of 'Biodiesel Quality':
I personally often used to fill my VW Bora (year 2000, engine code PD AJM, 85 kW) with biodiesel and also tried out various biodiesel filling stations.
I noticed that there were significant differences, even though ALL of these gas stations had the same pre-defined logo stickers attached.
The differences were so significant that at one (brand-name) gas station, the car not only smelled terribly of fryer oil and barely had any power; however, the fuel was hardly cheaper than 'regular' diesel. Then there was the 'free auto park' where the biodiesel was, for me, beyond any doubt superior. Not only did I hardly notice any difference in performance, fuel consumption, or starting behavior compared to regular diesel, but the price was also very cheap, being more than 15 cents below the price of regular diesel.
I haven't experienced any engine damage, clogged filters, or other unpleasant side effects in almost 100,000 km; however, especially in 'unfamiliar areas,' finding a good gas station can sometimes be frustrating; or you can simply use the good old standard diesel fuel.
This is just my opinion and is not intended to be the only correct one. Currently (with my 2.5 TDi AFB engine), I don't use biodiesel, but that's because the car is constantly in the workshop due to various problems, and I don't want to risk incurring costs if using biodiesel causes further issues, even though the vehicle is supposedly approved for it.
For me, everyone should do what they want; I've found a solution that works well for me, and I can only share my experience.

Stefan.