I can confirm that as a passive coupler, it works a lot better than nothing. But I eventually needed an XTB-IIR anyway once I had enough X10 transmitters (and effectively greater attenuation) in the house. I had no way of confirming noise levels before and after installation, so the baby monitor comment seems like useful information. I don't think it should be referred to as a "blocker" if all it does is slightly attenuate the signal. I wonder how likely it is for a neighbor's X10 transmissions to cross through a pole transformer and a PZZ01 and still interfere with one's system.
I got my power company to temporarily disconnect service to my house in order to install mine. It was not difficult to install and the only problems I had were with them. It took several form submissions and calls to explain to them that I wasn't moving or discontinuing service, I only needed it off for a day, I wanted it resumed at the same location under the same account, and I was doing to work myself. Strangely, they still opted to actually cut the cables rather than pulling the meter. And I also discovered that the cable connecting the meter box to the breaker panel had an outer sheath that was very good at being weatherproof, because it was full of water, as was the meter box since they had never put a proper drip loop in the cable drop from the pole. I demanded they fix that also before I hooked things back up. The contractor they sent out didn't believe me until I invited him inside and bent the cable over so it poured all over the floor. Making that happen required several frustrating calls as well, and they refused to replace my cable (since it's past their demarc) even though their negligence had damaged it. So anyway, be prepared for that kind of thing!