The premium versions very accurate I've never had any false positives with it myself. You can tell it to not block anyone in your contacts list and you can block or unblock blocks of numbers area codes etc. With the premium you're also getting a more granular description of the callers identity it has about seven different categories like telemarketer, debt collector, spammer, annoying etc If you're regularly getting annoying phone calls it's $20 well spent every year.
Oh and something to note that app is a bit clunky as it wants to be the default dialler but it's not necessary it can sit in the background you don't have to open it and it will block successfully
I found sometimes I get a call in and it's not marked and if I don't pick up I get an SMS saying no voicemail was left. But in that screen it marks that number as suspected spam it seems rather inconsistent
