I would say it probably has fewer movies, but it's selection is more mainstream. However it's model is quite different from netflix's (except if you have a paid for Prime account, with some titles).
The free prime streaming is only a subset of their catalog. It's also confusing. You'll click through to a movie and it will give you options to buy, rent in HD or stream with prime for free.
If you've paid for the account (in other words, it's not a free Amazon Student, or Amazon Mom account), then some of the titles will be available for free streaming.
I'm sorry, but I will have to call bullshit on that one.
I "installed" the app, which only took me to the website. I selected a movie and got a page showing their requirements page. It mentions "PC", Mac and Chrome OS.
No love for linux, at least not right out of the box.