Ha! I'd keep the kidney for now. You never know when you might need a digital back for the 501.
I bought the bellows from KEH myself because of the good price. On the camera it doesn't effect the handling very much as there is still plenty of room to cradle the camera without touching the bellows, especially with the 50 and the 150. Its a little awkward off the camera as I bought the cheapest one and the slide doesn't fold against the collapsed bellows, but it manage to sit ok in the top of my camera backpack. I like the fact I can use it with all my three lenses; the 50, 80 and 150. And it terms of shading the lens it's excellent - I think it really helps with the older (non-T*) lenses.