All of the above.
I have run one since they were first brought out. I ran one on my old Stage II TSE car, and I currently run one on my stock motor, stock t-body stock plenum car. It is proven to help redistribute the air flow equally between all the cylinders. The factory design causes the back two cylinders (#5 & #6) to run lean. This plate, whether it be for a stock plenum, a KB/Accufab plenum or a PTE plenum will dramatically help equalize the air flow. Each year at Bowling Green, Jason has a display that shows the effects that the Power Plate has on the various plenums. It is a very dramatic demonstration of a product that simply works.
I have also had customers who reported EGT temps that were within 50* of each other after installing a Power Plate. If you ask my personal opinion, every car should have one, unless it's a 9.0 or faster car (in the 1/4) that needs volume, or is running Stage II cylinder heads with a Monster turbo such as TSO class. Jason did his homework when he designed the Power Plates, and I've been a believer since day one. I've noticed on all the cars that I've run one on, that the motor idles and revs smoother, it's easier too tune the car and the plugs have a more even coloration compared to how they were when not running one.
Two thumbs up from me as well.
Just my O2's worth.
Patrick