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white is a funny beast, there's nothing that's a massive guaranteed advantage , I put that down to the pigment being titanium dioxide sounds expensive (as crazy as it sounds one thing the bridging coat will do is make the wall less thirsty= less paint used on the top/colour coats) I wouldn't worry about opacity. The tikkurila mentioned above is excellent in situation of dual natural lighting/ particularly awful ceiling surfaces, it somehow works on the texture it gives thus if used as a mist on filler it will horrendously flash the texture through especially if using a finish specific paint (f&b)
I could, but that would mean admitting I have nothing left in life. Not too worried about one coat and done. Just something that folks have found covers better than others. The Leyland trade does the best of what I have tried, just curious if there is anything even better.