The Bender 4x5 is the first 4x5 I owned. If you take your time and are very careful you can make a pretty decent camera. It is stable after a small change to the tensioning mechanism. I made some "washers" out of 600 grit paper. I'll have to replace them eventually but so far they are holding a little bit better than just the plain friction of the metal washer on the wood.
There are some differences (looking at the pictures) between the 8x10 and the 4x5 but I have the feeling the 8x10 will be a bit more floppy.
I've been very happy with the 4x5 and it looks nice, works great. In the pre-manufactured 4x5 kit category there is also the Bulldog. Bang for the buck, the Bulldog doesn't look quite as useful to me. The Bender has a tremendous movement range and plenty of bellows extension, more is available in the bellows than the stock rail allows.