Pretty much. At my undergrad we had a similar set of aluminum cable hooks permanently hung on the truss we used. They're just as simple as the picture makes it look and because of their shape and the way the cables drape through them, they won't fall off the truss under normal movement. It's dead simple to move them around as needed and they cut down on a lot of the tie line you would be using otherwise.
If you've got a truss that you rehang often, I'd recommend looking at a set of cable hooks (either these or other ones). The cables aren't dressed quite as cleanly as you can get them if you go all out with tie line, but they make the cable cleanup process dead simple.
I can't speak to whether these particular hooks (or any others) would have a published WLL. As long as you don't go wildly overboard as you load them up, I wouldn't worry too much, as the alternative is tie line or electrical tape. I'm not sure how beefy or expensive the plastic hooks in your picture are, but City Theatrical has an aluminum version that runs around $17 online. I trust CT's name and reputation, and to my eye, the geometry and material of the hook look better. Looks like there's a pretty decent variety of other manufacturers in aluminum and plastic with different designs if you go digging around.
As far as spacing, 3' is probably a decent starting point, but I haven't used these for a few years and I can't remember clearly how far apart we were able to use these.