I usually fly Air Canada (AC), where these have been more common than the us carriers i've been on for a while. I use it _every time_.

Do I also have a phone? Sure, but the screen is smaller and I have to hold it. Do I also have a laptop? Sure, but if the person in front of me reclines quickly I don't want to hear a crunch.

In economy I'll use the in-seat thing to watch something, and leave my laptop in my bag. In economy-plus or higher I'll put a movie on the screen and write some code on my laptop.

On the AC flights I've taken I'd estimate something like 80% plus of the folks on the plane are using the in-seat stuff to watch something. The rest are asleep or reading a book.