I bake and eat sourdough but need to inject lots of insulin: in my experience, it does not reduce my BG.
Unfortunately, apart from taste, I have found no benefit over un-soured bread.
I do eat it sometimes just because I love it! It doesn't seem to impact my BGs any more than the lowish carb bread I normally eat so in my experience I can't say I notice much of a difference. But we are all different and you probably need to try it yourself to see what effect it has on you! And no, it doesn't lower my blood sugar, but seems to have very low impact.