The good news is that this service means you can create an
"allow" list of approved callers.
The bad news is that in addition to being a slow and manual
process, this solution works by hanging up on every single
caller not saved to the allow list.
So if your doctor's office calls from a number you don't have
saved, she can't get through. Same goes for the pharmacy or
the contractor or even the pizza delivery guy.
This means that you will miss a significant number of calls
that you actually want, and even need.