Totally agree Ajax about your thoughts here, i've been using this method and all the others for years and it really does work on the right job.
As i say you don't just spray it, it needs to be worked in so you can do that as you cut in. Obviously you can't use it in someones new kitchen!! But then primer on rollers, sponges and brushes aren't the most splash free method either.
I use a hand sprayer or the larger pump sprayer (green ones £15 B&Q) for big floors.
But some things have to be rolled or sponged, ie Mape Ecoprim grip etc.
I could be very wrong, but with a sprayer you could spray on to anhydrite for example a light coat, then back roller it, this way you can control how much is being applied, with a roller or a brush, you tend to slap a big dollop on and then push it around, which in my opinion could over saturate the substrate. If the floor looks like it needs some more priming, its very easy to do again, you can do it standing up and it gets done much quicker.