Any positive experience with it?

Of course there is)) I'll tell you that I had a problem - the sink was clogged and when I pierced the drain of the sink with a plunger, the water from the sink went into the shower. The sink was cleaned, and there was a dirty dregs in the soul, which nevertheless gradually disappeared. We searched for a reason for a long time, then a friend said to try to install a check valve. Installed through Pom Waterproofing www.pomwaterproofing.ca/back-water-valve-installation/. The situation improved immediately) Therefore, my experience is only positive. But I do not rule out that everything is individual.