I tried leadbelcher and mechanicus standard grey spray. both require a primer to achieve a good coat. The paint didn't stick and pooled in the recesses.
I also tried Caliban Green and Zandri Dust. they worked well on my Land Raider without primer, but also looked good on a primed model.
Conclusion: might depend on the color or the can. The owner of my local GW store told me he uses them all as primer.
Best thing you can do is a) try it on a spare plastic model / some left over sprues and b) always, ALWAYS, spray as thin as you can and make to coats if necessary. You should be fine.