Geek-freak, I've never seen an SBS - so I'll take your word for it that it gives "almost full picture of the traffic situation in real time with something that comes pretty close to a real radar display"
another aspect of the traffic picture which no-one has mentioned yet, (and I'm pretty sure you can't intercept/see???) is CPDLC messages [Controller-Pilot-Data-Link-Communication]
I often get pilots in my airspace saying "gee, it's quiet" - I have to tell them that actually I have 17 planes all 'email-ing' me via CPDLC [even though they are well withing VHF coverage!] and actually I'm pretty busy!
as for being watched, like the other's said, Big brother is always watching! It goes with the territory.