Prefs and Docs - UDiff should have a link back to Diff Viewer section
Tortoise Git preferences, TortoiseGitUDiff section
I think that both TGUDiff section and TGBlame sections should have a message (or even an active button? a hyperlink?), that whether those programs or there replacements are being used is settled in "Diff Viewer" section.
Because it is not that obvious for newbs, they open TGUDiff, from within they open Preferences - and then they have to spend quite a time and effort to find "where is the very running of those programs is tuned?". There is to be an instant hint where to go to use this program or a replacement.
Same applies to the documentation. Four places in total.