I've used a Finnaren & Haley paint for a screen.
Before going with the paint I had ordered material samples from Da-Lite and Stewart. The Da-Lite samples arrived first. They are small samples mounted on 8.5 x 11 pages. Frankly, way too small to evaluate performance.
Do not ever try to do side by side comparisons of screen material, it won't work. First off, the projector needs to be re-calibrated for each material. Second, the side by side comparison creates bias which messes with the brain. We see the brightest white as white, and the darkest as black. A side by side will invariably make the white on a darker material seem gray, whereas, viewing just the darker material white will look white. It's hard to explain, just take my word for it.
The Da-Lite High Contrast grey material seemed to be just a flat grey with no real special reflective properties.
I took the sample down to the store and matched a paint to it, hoping to be able to get an entire surface of that shade so that I could do a better analysis.
I did a few things. First, I prepped the entire wall by rolling on a watered down Sheetrock joint compound and skimming it with a 12" knife. First, down, then across, then down again... allowing drying time in-between. This technique covers years of roller and brush marks and various imperfection in the wall surface, resulting in a super smooth and fresh uniform surface. (I have sheetrocked many entire rooms and had a lot of previous experience working joint compound. It might be difficult for a first timer to archive acceptable results.)
While allowing this to age (about a week) I watched images projected on this surface. It was actually usable, but lacking somewhat in contrast. After aging it for about a week, on went a coat of Finnaren & Haley T.D.C. Primer Sealer.
I use Finnaren & Haley paints because I like their consistency. I have never been happy with those from Home Depot, feeling they were too thick. To avoid hot-spotting I wanted a very flat smooth surface, and I find the thicker paints do not achieve this as well.
The screen area was masked and then rolled using two coats of a Finnaren & Haley Low Luster Interior Latex base, color matched to the Da-Lite HC sample. The mix was a B8 L12, which relates to the amounts of pigment used.
For the record I'm using this with the JVC G15 at an 18' distance. The screen measures 100" in width, and roughly 48" in height. This may seem like a strange ratio, which it is, but I selected it as a compromise. I run 2.35:1 slightly shadow boxed, and the other ratios pillar boxed.
I have found that when I place the Da-Lite sample in the center of this it virtually disappears - I can't tell the difference.
Shortly after all of this I received the Stewart Grayhawk sample, which is much larger. The Stewart sample has very different properties. Fist of all, it is a lighter shade of gray. The blacks seem washed out compared to the Da-Lite and the paint... what did I say about side-by-side comparisons. The Stewart sample also differs in that it has a special coating which seems to yield brighter whites.
My concussions thus far are this:
Paint will do the same thing as the Da-Lite HC at a fraction of this cost, and is far more flexible.
The brain largely adapts to the black level afforded by the projector/screen combination. Unless I do a side-by-side I would never see the difference.
The room needs to be dark, regardless! Before you even turn on the projector, look at the screen. If it doesn't look black, neither will the image - especially if there are blacker objects in the room which will re-calibrate the brains idea of black.
While I set out with the paint as a cheap way of evaluating gray shades, I've become quite accustomed to it, and as a result, have no near term plans to purchase an expensive screen... maybe someday.