Regarding 2 cats or 1.
I honestly think this depends on the cat's personality.
Some cats love the company.
Other cats really change and get all freaked and territorial and it just causes them more stress.
It's not the end of the world for them. But I can sense that they just aren't as happy and some will NEVER get used to it.
Cats sleep a lot anyway.
Assuming you aren't away for ridiculouosly long stretches and perhaps can be content just looking out the window at birds or trees or whatever that they might be okay.
And now I'm going to spam one of my sister's products. I don't even know if she is making any profit from this thing anymore now that Target and PetSmart picked it up so it might not even be spam.
Personally, I don't think it's very good (so-so production quality and sound) and my cat wasn't interested in the least.
But other cats respond extremely favorably.
It's a continuous loop DVD showing birds, squirrels, fish, etc.
Some cats really really love it.
And the owners feel better when they leave their home when they are able to put something on the TV that their cat actually will like.
link