CBS is the worst at this. I accidentally deleted a few episodes of Person of Interest this season, and figured I would go to iTunes or Amazon to buy. Yet, they don’t have season two, and if I recall not even season one for digital download. So, I took to piracy to get the few episodes I missed.
They mean using devices all at the same time. I use an iPad, Nexus, two phones, a PS3 and a BluRay player, plus a few laptops. You can have an infinite number of devices, but the price increase is to use four at the same time, currently only two can be used at the same time. Also, computer is not included in that count.
I’ve had mixed reviews just from getting my Ultra Vilot copy from a DVD/Blu Ray I bought. A movie worked just fine in getting my digital copy, but had so many issues trying to get the TV series I just gave up and didn’t get the digital copy.