I ran in to a couple problems when trying that script (details below), but I'm really happy that you shared it, because I had not seen ':windo diffthis' before, and that method of scripting diffs. I'll definitely be customising it!
(I found that my mac machine doesn't support the '-printf' option, and also I was attempting to run 'git bvd main' on a branch but it seems it does a recursive directory diff, so I'll use 'git diff --name-only' as the input to the awk command).
Edit: worked nicely! I haven't used tabs much in vim so is a slightly new workflow but otherwise very handy