Paul1977:

 

Yep, any decent size cat looks ridiculous going through it. They can do it, but our bigger cat (not fat, just large male) would have to kind of "superman" his back legs and pull himself through with his front ones. When we shifted we got the larger one. Much better (but a significant price difference just for some extra plastic).

 

for the tech that is in them I am surprised they are as expensive as they are. Also, you'd think there were alternative knockoffs all over Aliexpress, but I can't seem to find any - so maybe they are more complicated than I think.