I have used Multiple Customfields Filter for Virtuemart for an eshop few months ago. I choosed it for its good price. I was very satisfied ! ! They helped me customize it to fit the template of that eshop. Since then I used it on every eshop that I build. It works w/o any problem and it's very customizable. On top of that their support is excellent! They have answered all questions within 24 hours or less no matter how complicated they are. They are really very experienced and extremelly helpfull.
I highly recommend this extension and the guys behind it! ! !