It's mostly whether you like BBEdit as a diff tool, I'd say. Any GUI diff tool is an advantage over just using git straight, and since you already have BBEdit there's no reason not to use it -- it's better than many others I've used.
(Having said that, I actually use Kaleidoscope as my git diff tool, mostly because I use it as a git merge tool: BBEdit can't do a three-way merge. But I do use bbdiff from the command line on occasion, and I've been using the "Compare with..." functionality in the new Git menu in BBEdit 11.1 frequently.)