I think you may find matte medium even more expensive. Re the WS cement, if it dries faster that may be a handy feature. I generally ballast in the evening, work on something else for a while if its not to late when I'm done, and its dry next morning, so for me drying time isn't important. And I have the white glue around for other things anyway. Concerning making a mess mixing it, or correct volumes, I keep an empty white glue bottle handy, I'll pour white glue from a new bottle between 1/4 and 1/3 full, then add water till not quite full, cap and shake. No mess, no fuss and exact ratio doesn't seem important, always dries with good bonding capability. The ratio is more important if you attempt to spray it, though I'll never do that again. Using the bottle to apply is so easy, and much neater! No need to cover things you don't want the glue on. And you can keep the mixture you don't use for at least a couple weeks in the bottle, just shake well or perhaps add a bit more water the next time you use it.
Gary
Gary