I believe that paint has primer in there also.
One thing with paint that has primer in it as was mentioned,is it dries fast,plus when cutting in with a brush it is difficult to work with.
If your room is primed already why spend another $20 a gallon for primer/paint you don't need.
If your slow at cutting and rolling I'd advise against using it,paint that dries to fast won't look good at all.Guaranteed you'll see your brush cut lines and perhaps some roller marks if you don't catch them.
Been painting for the last 25 yr or so,doesn't work for us,prime,sand 180 grit paper should do for a smoooth finish.
Laundrew,BUY A PAINT STRAINER FOR YOUR PAINT,if you don't even new paint has small chunks and lumps and you will have rough walls.