So I use Now TV through my TV's app not a Now Tv box. And yes it's pretty good. But am I missing box sets etc. The US has only 20 or so box sets, the Uk about 12 or so. When you look at featured etc it show NCIS with only 4 episodes and Blue Bloods with like 3 or so, never complete series. So is the App cut down?

No you are just looking in the wrong place, the US/British Box Sets / Must See etc. are just part of the highlights section of the menu.
For the full list of shows, scroll down to the bottom of the sidebar and look in "All TV Shows" or "Channels"

Some of the TV series content might be only available for 4-6 weeks

Yes I understand some are on timers etc. But I caught a sky advert the other night telling us how many box sets they have. I know Now TV isn't directly linked to Sky, but would like to see more box sets, there's no Billions, Ballers etc

Ballers is on nowtv all episodes under entertainment - channels - sky atlantic. Also Billions is there too.

Yep, does seem like you're missing some. Just done a screen print of the US and UK box sets currently live, and I'm showing 36 US box sets and 40 UK box sets.

As gother mentioned above, Ballers is showing in the US box sets section. However, some programs like Silicon Valley have all episodes from the first two series, and 9 from the current series three but is not in the box section area. Also, take for example the excellent Gomorrah which has 2 series, but as it's Italian this doesn't appear in UK or the US section.

Have you tried using the search function? Both those shows you've mentioned show up on AppleTV .

Yep my apologies, it does seem there are more as mentioned if I scroll down to All TV Shows, and yes I noticed that Ballers was in fact in the US Box Sets box.

The NowTv box, iOS app, and appleTV app are all great once a show is in your 'my shows' or 'recently viewed' but finding and searching for shows can be a pain.