The toilet also flushed really well and hasn't gotten plugged up even once yet, but I made sure to have one that would work as soon as the toilet was ready to use.
(USA) - I had the same issue as the user above due to a high efficiency toilet. The opening is more rectangular/ elongated than a normal toilet's circular opening.
The exit hole is recessed backwards and squareish, with a wide channel. The flange doesn't sit properly inside it, and the circumference of the bell is too small. With the beehive the circumference is wider, and it just sort of smothers the whole area, and pumps the water through its center hole, which has nowhere to go but into the exit. Like, it's not anything precise, it would probably work great in a "normal" toilet just as well because it just fills whatever space there is.
Basically, it's shaped weird and won't make a seal. It's a WaterSense toilet that flushes very efficiently with 1.28 gallons, with an unusual configuration of input/output under the water. Almost like a channel from front(ish) to back. If you try to use a plunger like those pictured, part of the channel isn't covered, so you just push water back out into the bowl. Good thing I was trying it with a clean new toilet! The wide deep beehive shape lays rubber all into the space, pushing the water down into the exit hole.