Either side does not block the view fully, at least not at after dark with the lights on as I found out to my embarrassment! I took the dog out one night and was horrified to see right into my flat as if there were no blinds up at all. Hard to describe which way but as others have said, try each way after dark and go outside and look in with the lights on. Best way I can describe is you need the slats pointing upwards and slightly inwards into the inside of your house.
I've been outside and looked in with the lights on I can see some but not clearly, I have noticed with the slats up, I can see outside through gaps in the slats about a quarter of the way up the blind, its as if they dont close properly at the bottom of the blind.
....it's simply the angle at which you're looking through them. If you stood on a stepladder and looked through the upper part of the blind, I think you'd be able to see through there as well.