I installed PB1 for this reason alone, and let me tell you any bugs I've come across are nothing in comparison to the robo calls.
Though I honestly expected to not have any kind of notification when a call was blocked, or maybe a section in settings where I could review any numbers that didn't make the cut, but it doesn't perform that way. If you didn't know, your phone doesn't ring of course, but the display lights up to say "Missed call". Not a big deal if your phone sits in your pocked all day but sometimes if I have it on my desk at work I'll see it light up and curiosity gets the best of me.
You should be able to turn off the notification for the missed call. I haven't tried, but now I'm going to have to try to see...