When I was a fill monkey at a dive shop that filled nitrox via pp blending, you can be damn sure I required a new O2 clean every VIP. I have no idea what you are doing with your tanks, all I know is that it was O2 clean when it left the shop after the last VIP. And O2 cleaning was a ~4 hour process, so it wasn't cheap. That shop really wasn't set up for nitrox though.
It's my life and limbs on the line when I'm filling, so if you don't like it, get your own compressor.
Or go some place with a membrane/bank system.
-Chris