Hi guys, I'm new on here.
Cementone Plasterers Stabilising Primer is what i tend to use, Value for money, the grit is not too coarse and won't eat up your skim and i've never had any issues.
Also used Thistle Bond-It but its more expensive and only available in 10L tubs.
Feb Bond Blue grit is probably the worst one i have used as its tends to clump and be either really gritty or too thin on the grit front.
PVA is good if you are on a tight schedule or price but if applying to a variety of backgrounds with different suction it can be a nightmare with some going off quickly and areas tending to hang wet and slide!
Just sharing my experiences and opinions!