If you have a look at the manufacturer’s website all the figures are there. I’m using a FOSG2 (circular version).
Off the top of my head it’s the transmission that is the problem. It’s only about 37% thus you’re losing ~ a stop. A fast lens is needed. The extinction ration is 1800:1. That’s dark enough for meteor work but whether this is sufficent for other imaging I’m not sure. The meteor image shows quite a clean profile, I pleased with the result (and if I’d paid more attention to the timing diagram on the website the actual chopping rate wouldn’t have been a surprise! ;-)). I’m currently constructing a ye olde fashioned rotating shutter for some other cameras so it’ll be interesting to compare the results….