Comparing PPFD of different lights is a suckers game and gives lighting distributors an edge in selling you a light. A PAR reading grid can help prove to a potential buyer that PPF is as rated, but in general, it's easy to be tricked by PPFD.
What matters when buying a light is not PPFD, it's PPF. (or watts of PAR).
PPFD can be made higher by packing the light in a small area (spectrum king) and using optics to focus it into an even smaller area.
It's true that PPFD is what the plants care about, but when buying a lamp, you should consider PPF the most. Watts PAR is essentially the same thing given similar spectrum, and it's easier to calculate, so just use that..