I have a Texas Instruments calculator from the 80's that has the same feature. Brilliant. I wish we could get stuff like that for our new tech.
And yeah, those are pretty good descriptions of each.
I like cases that just protect the back. I have a few covers too, but only because they double up as stands.
Sleeves tend to be made for a snug fit and I don't like that aspect of them because they put too much pressure, especially on laptops. Plus, they're kinda stupid, especially for laptops and tablets because they don't keep in mind that you might want to take the charger along with you.

So you have to carry another bag just for that, or be like me and carry them in your coat pocket.