Yes, although you can already do that in the normal immigration line, as long as you are a tourist.
No it is a tourist entrance visa, its valid for one entry. When you come back as a tourist you can get another 6 months.
I dont know immigartion status for other countries. BUT UK passport holders get 6 months visisor visa entrance to Hong Kong. Every country is diffrent.
This sticker is no different than going thorugh normal immigration as a tourist, it just speeds up the formalities.