Further update on 4kave.com: Had "Three Billboards" in queue. It took about 8 days to receive the disc after I returned "Shape of Water". This time, it came in a "Netflix" type return envelope, everything except the disc sleeve and prepaid postage (it had a first class stamp).
However, I have recently received an email from them. Apparently USPS has been difficult, breaking/losing discs and raising prices. So 4kave eliminated the lowest price tier, and the cheapest plan now is $15.99/month. This includes unlimited rentals, but one at a time.
I have cancelled my subscription plan as there are better options. So I am trying 3d bluerayrental for 4k discs. I'll start with a la carte rentals and then maybe move up to a monthly subscription.
And of course, still waiting for Redbox.
There! I've run circles of logic around you!