OK, now you're changing the parameters and trying to apply my answer to it. Your question was: "...unless I can get a fully yes or no answer as to whether or not this particular bivy (REI Minimalist) is 100% waterproof..."

It's not. It can't be with a big mesh hole over the face. Thus, my answer: NO.

Now, it appears you're wanting to take that very specific answer and make it my answer to the use of bivies in general. You can't - go back and read my earlier post. In case you don't care to do that, I'll summarize: there are waterproof bivies out there; the Minimalist is not one of them. They'll only be waterproof until you open them in the rain to get in or out; then water will get in - unless you use it in combination with a tarp.

I'm not interested in starting or feeding a argument, or making you any more irritated than you appear to be, so this will be my last post on this particular subject.

I encourage you to make your own decisions - that's what I usually do. Good luck in finding the shelter that's perfect for you. I found mine: MSR Carbon Reflex 1; I just spent the whole weekend hiking in the rain and sleeping in it in the rain. Not a drop got in on its own, and there was no noticeable condensation, even fully buttoned down (though wet rainsuits, etc., did make the inside a bit moist - no way to avoid that.)