Yes I have the NPC 72x72(using 4x5 Pol sheet film), I use it almost always to proof my shots, or to use Pol55, what will disarm you at first will be that the image isn't square, it's kind of 'lopsided', where the image kind of spills over the 72mm margin in spots, other than that, it's great to use, the area is way bigger than 6x6.
Get one in mindt condition, so it fits flush/tight, some folks have driven over theirs w/a truck, then dribbled the back like a basketball, and then they sell it. You get the idea, some Mamiya stuff has been through the wars.
You get a good one, your good to go 'till the end of time'.