So far, I've been using my FS100 either with the Heliopan VND filter, or with my hefty RR mattebox and 4x5.65" ND glass filters. Now that I've bought a smaller/lighter mattebox (MB-600; nice), I'm after 4x4 filters. Never used anything other than glass filters, so have no experience on the picture quality using resin filters (and perhaps stacking 2 such filters). But the fact is that for a price of a single Formatt 4x4 ND glass filters, I can buy 3 Hitech 100 ND filters, so I'm a bit lost...

I'd be grateful for sharing your opinion on the quality of resin filters in general, and the Hitech brand in particular. Also, will a typical 4x4" filter tray accept "system 100" (100x100mm) filters?