4k is fine if you have a 4k source to watch, but bear in mind that for that additional resolution, something has to be sacrificed somewhere else so the pictures will be more highly compressed.
If all you watch is freeview for example then think carefully before spending your money on it. Most channels are still broadcasting only in SD right now. And quite honestly, even if they all converted to 4k tomorrow, the compression would be terrible - it would have to be in order to get so much data down whichever route you receive it. You might have 2160 lines of resolution, but it means nothing if the footage has been compressed so badly it looks like it's come off youtube 10 years ago.
I work in telly. The industry has just spent millions and millions of pounds upgrading to HD in recent years. 4k is a gimmick at the moment aimed at consumers with nothing better to spend their money on. The industry won't be spending millions and millions more to get rid of what they've just bought and upgrade again. Sky may be doing a UHD channel (just one, I believe), but don't expect that to increase anytime soon, just the same as there's only very limited 3d content on sky and no major push in recent times to increase it. 4k needs 4 times the data at the same compression as standard HD pictures, and that is 4 times the data of SD pictures. a 4k channel would therefore basically take the bandwidth of 16 SD channels... That's why you won't see it on freeview anytime soon...