I kind of rolled my eyes when I saw people trashing the idea due to bead size, and comparing it to the commercial material. I think if you get the smallest bead size you can find, within reason, it will work fine.
Two things to consider; One is that the commercial screens are designed with FILM in mind, which has (nearly) unlimited resolution. Large beads could degrade this somewhat. But in home theater, we have pixels to deal with, which are many times larger than the tiny beads. If the effect of larger beads is such that it smooths out the transitions between pixels, it could actually be a net gain. Second, when using paint to anchor the beads to the screen, smaller isn't going to be better. Smaller beads will have a much better likelihood of being swallowed by the opaque paint, rather than staying on the surface where you want them. Again, the net result would likely be better with the larger bead, with this method of application.