I own two of these. When small game hunting/varminting I carry my AR vertically with a traditional sling. Having the low profile (these barely extend from the mag well) makes it quick and easy to get the rifle into shooting position and on target. 30 and even 20 round mags can hang up in your clothing or armpit.
There are no magazine limits in my state but 10 rounds is plenty for the hunting I do, usually 1-3 shots total. If you feel like you could use more ammo you can fit a 2nd mag in your back pocket. One of the main reasons I hunt with my AR is it's lightweight and easy to carry so I like that these mags are light and compact with plenty of capacity for hunting and varminting.
The other use where these mags excel is for load development. I'm usually shooting 5 or 10 shot groups to compare loads. Regular capacity mags sometimes stick down too low to shoot prone or from benchrest with bags and cause a weird pivot point. These allow you to support the end of the handguard and the rear portion of the stock without a long mag interfering with a stable rest.
Also you can store them fully loaded because the clip takes the stress off the feed lips. They are easy to clean as well. I really have nothing bad to say about these mags.