Hi Lefteris!
It is very sad to say, but your solution not for me (K2 2.6.2). I created menu points with all my categories, (single point to single category). After that i still have descibed problem. The problem is actually a bit bigger: in the exampled link mywebsite/component/k2/itemlist/category/1-review i can change any part of it except Item ID and will not get 404 error, although i must get 404 cause of wrong link!
I hope, i do something wrong, and you will find a solution without problem.
I posted in another thread a
hack
, which helps out with this issue and avoids duplicated urls/not given 404s. It is a dirty hack, and i hope, you will easy provide a more smart solution. You know all about your K2:)