Nope, never used it, my preffered primer for difficult surfaces is Benjamin Moore Stix. All their products are brilliant. Not cheap though. An excellent alternative is the Zinsser range - coverstain sounds like the one for you, but 123 is pretty good too. What surface are you trying to paint? I'm on my phone at present but if you want to ask more then feel free and I'll reply when I can and am home..