Just a quick and dirty list for myself. When I was looking for hexeditors with a file-compare view, these came up. All three of these options seem useful in slightly different ways.
vimdiff and :%!xxd
Vimdiff just calls vim with a bunch of preset options.
vimdiff file1 file2
Once inside, you have to convert each file with :%!xxd and then after making any changes, convert back with :%!xxd -r before saving. Slightly clunky, and I’m sure there’s a way to automate all that. But I was only making select changes. And a few keystrokes isn’t so bad.