In regards to the ProComp bbc heads that I have personally worked on, half were outright unacceptable, and returned. Of the sets that were kept, most needed considerable rework. This includes valve seats that were up to .025" off center of the valve guide. Also heads that had varying seat depth (stem height). Several heads needed seats replaced due to excessive depth and seat contact area too wide. Most of the time, the machined dimensions were consist from cylinder to cylinder in the same head, but varied too much as a set. I suppose someone could buy 20-30 sets and end up with 5-10 good pairs. But, unfortunately for the customer, shops don't work for free. The appealing low purchase price is soon gone due to needed rework. When you're all done, you're close to the price of Dart/Brodix/AFR, and the quality still isn't there.
Now, ProComp problems that I have personally seen, but didn't work on include valve spring seat pocket breaking through because of lack of material, which was caused by casting core shift. This occurred on a head that had springs for .635" lift. Also, a pair of heads that varied 3 cc in volume from head to head. These problems were observed at other shops, and then can complaints of many more additional problems with ProComp heads. I guess you could call that "lip flapping".
This topic was started with questions regarding using Pro Comp heads on an engine in the 700-750 hp range. I highly recommend staying far away from Pro Comp.
Finally, relate to us the personally experiences you have had with Pro Comp heads. How may sets have you worked on?
In closing, this is my position. I will set a customer Dart, Brodix, AFR, even Edelbrock. But I refuse to sell anyone a set of Pro Comp heads.
But then again, my customers don't race printed flow bench numbers. Maybe these heads are a bargain for bench racers.