I've owned and have experience with just about every type of screen ever put to market, and I presently own a SI Black Diamond 0.8 gain gen 3 screen. I just got the Cinegrey 5D sample the other day (small 6" x8" only), and did some comparisons vs my screen, other SI BD and standard white and HC gray samples.
First, I think the Cinegrey 5D shows promise, and does some things well. It's close enough to the neutrality of a good white screen - if a little on the green side, color temp wise - but it's a bit darker overall than a good white screen, and highlights aren't quite as bright, even more subdued/grey. In this regard, it's probably like most gray screens, which need a boost in contrast controls to make the image pop. It's probably bellow a Stewart firehawk in this regard, too. Black levels are really good better than Firehawk and 1.4 gain Black Diamond - by a smidge), and just short of the black level champ, the 0.8 gain SI BD screen. Color and overall image seems to have some sparkle and life from the gain of the screen, and color saturation should be fine. Although, ultimately, the SI Black Diamond 0.8 and 1.4 gain screen materials are clearly superior in the contrast department, and white level is clearly more punchy and bright on the Black Diamond! - overall, the dynamic range on the BD's are unmatched, in fact!
On any given average projected image, I think you'll find the SI Black Diamonds offer a wider dynamic range between black and white, than just about anything you'll find - but they're expensive!! Another mark against, if any on the more expensive BD screens, is that there's somewhat of a "shimmer" to the image, (which is better than old BD material Versions 1 and 2, however), which is visible in bright/light/white images. Not a deal breaker or unworkable, IMO, but it's there on the BD - possibly less of a nuisance on a very large screen,and way less noticeable in a room with lights on, I suppose.. The Cinegray 5D showed much less of this artifact, from neutral.
I think the Cingrey 5D, for an more affordable Light rejection screen, probably will prove to be a good choice, and work very well, is my thought. In fact, I'm likely going to try one out. I can use a couple screens in the house.
So far, however, I think this screen should offer all the benefits that a good light rejection screen should offer, with workable downsides, on a budget. Can compare more later should I acquire one.