I would love to have a GS-1 style grip on my Mamiya 645 Pro TL. For those who're not familiar with them: it features thumb-powered film advance, so it is much more lightweight than motorized grips. But it offers much better ergonomics when shooting with a prism. Something like this would have been perfect for a lightweight 645 SLR like the Mamiya 645 Pro.
I have no idea if it fits any other camera besides the 'E'; I think they would have said so if it did. The shutter release linkage looks a bit clunky to me, but it may work perfectly.
The really old and clunky power winders for the original series of Mamiya 645 cameras will apparently work with the 645E. So perhaps the GN401 will work with them.