Are Category III/IV movies legal to watch?
This depends on which country you are from. Other countries in the region (most notably Malaysia) heavily censor their movies, and Cat 3/4 movies are illegal there. Most western countries are fairly lax about Cat 3 movies. However, any kind of hardcore (sai chai) movies would fall under local censorship laws. Even the most tolerant countries like America have put restrictions on the kind of films one can view. Though I have not heard about any Hong Kong product being banned, certain Japanese movies have been, since they depict rape or other sexual acts deemed “obscene”.