I shoot a fair amount of 4x10 with my 8x10 camera and really enjoy the format. My camera has the grooves in the back for "splitter" boards. I do not have the original splitter boards, but have cut my own from flat sheet metal and painted them black. With the splitter I have no need for a ground glass mask or a split darkslide. I keep track of which half of the sheet has been exposed in a notebook that I carry. So far I've only screwed it up once.

With the grooves & different sized splitters I can shoot 8x10, 4x10, 8x8, & 5x8 all with one back & 3 small pieces of sheet metal. They're really quite handy & extremely cheap.