I've only been using these for a few weeks and so far they work well. I'm not sure what the review was referring to it not working on newer toilets. My house is only a few years old and they installed with no problem. No smells either.
I bought my first one on a whim just to see what it was like. After years of disappoints with blue water the discolored the toilet, wires the fell into the tank and jammed the ballcock, and products that affected the tack mechanisms I was intrigued with this product. Simple, functional, and a nice clean smell in the room. The tablet last as predicted.
A few years back we found out about the product and tried it in our toilets. It eliminated the brown (iron-based) sediment that used to collect in the bottoms of our toilet bowls as well as the awful spotted black rings at the water line in the bowls. We used to have to clean every third day. Now we clean once a month. Uses the "bypass" so doesn't destroy seals in tank. We are on a septic system and it hasn't adversely affected its operation so we are pleased as punch.
We have low flow toilets and it seems I was always cleaning them because of the black gunk buildup under the rim where the water flows into the toilet bowl. This product really does work in keeping every thing cleaner as it is installed in the tank (two little bleach tabs go into a little container that attaches to the hose where the water comes in so the water washes over them before going into the main toilet bowl - a bonus as most tabs that go into the tank sit at the bottom making a mess as they dissolve). So once you purchase the beginners kit you just put two tabs in the little container and walk away. Still have to clean the toilet but not nearly as often. When you flush there is a slight bleach smell each time (just pointing it out in case of any sensitivity)