I love Breakthrough. i do all my kitchen cabinet jobs with the stuff and it looks great. Very durable as well. I do a lot of work ie. wood stain trim going white and most of my cabinets are wood stain going white....but if your using white Breakthrough the woodwork sometimes will yellow on you....like yellow stains that come through the paint. So, you need to prime or seal first unless your using a darker color. Dark colors hide the yellowing.
I have sprayed a large built in poplar bookcase with no issues at all. The wood was a bare wood and I put the BT right over it...but I now use a wood primer on bare wood simply because the primer is cheaper and I don't need to use as much BT. Also, some primers like SW wall and wood primer sands really nice.
MDF, I never sprayed MDF before but i heard if you do then you need to thin it down a little but that is not from my personal experience.