EDIT: pay no attention to the text below, I have misread the linked documentation. uBO isn't using external proxy for any network requests.
Not sure how much -- or at all -- you're involved with uBO. Your name does ring a bell though so I'd like to remark to you that making the users' browser use proxy is a step too far. It shouldn't automatically be enabled.
A privacy extension should do everything it could locally and stop there. If I one day figure it's not enough then I'll set a privacy VPN (or use an existing one).
I don't want that decision made for me on my own machine without my consent. :(
And apologies if my comment is misguided -- I only skimmed the linked page and I might have misunderstood.