I bought one from him a year or so ago. Excellent service and very fast shipping to the US. I was replacing the factory supplied gg on a 7x17; the GVB gg was brighter than the factory gg, and I found it slightly easier to focus. I was very happy with the grids on the GVB. (I think he calls them lumigrids?). If my GVB gg broke tomorrow, I would buy another GVB.
I made an order in jan. was told 6 week delivery time, no ground glass arrived. He blamed the post, was told that he sent another ground glass, but still no ground glass. I sent Geert a mail to cancel my order and send the money back, no reply. So be very cautious doing business with him (sheetfilm.be)!!