I've tried the Vallejo White Surface primer and it's not very easy to use brushed on. It's very streaky (for want of a better word) and is probably better suited for airbrush (which is what I use it for).
Just got a bottle of Badger Stynylrez and it is much better as a brush on ... just haven't gotten around to airbrushing it yet, which is what I got it for in the first place.