If he already has a talk talk box it'll still work if he leaves talk talk. He will loose the talk talk player but will still get all the freeview channels.
If he moves to BT they have a smaller, much faster Youview box which is very good.
It will continue to work but just goes to the basic freeview mode with no pay to view etc. People buy them cheap off bay and gumtree from people who sell them on. The BT and TT ones are cheap.
I have one of the newer ones and its very good.