Last bit first: No engineer is required. It's basically 'plug and 'play. (There's a bit of fiddling around with setting up an account first but it's fairly straightforward).
At its most basic (i.e. without purchasing any 'passes') a Now TV box turns a 'non-smart' TV into a 'smart' one. (i.e. it provides access to catch-up services, such as BBC iPlayer, etc and has a few other apps too, such as allowing users to watch Youtube videos on their TV sets).
By purchasing 'passes' though, additional functionality can be added to it. There's no contract involved, so you can buy passes as and when you want. (If you buy monthly passes, they auto-renew but you can still cancel at any time).
However
regularly using Sky Sports Passes with a Now TV box can be an expensive way to watch Sky Sports. A 24-hour pass (providing access to the main Sky Sports channels) costs £8.99. A 7-day pass (again providing access to the main channels) costs £14.99. A one-month pass provides access to all 11 channels for £33.99. There's also a football season ticket, giving you 128 Premier League games and 138 Sky Bet EFL fixtures , over a 10-month period, for £199.
https://www.nowtv.com/sports-purchase