The $20 CoverBuddy is a slim rubber hardshell case that works to protect the back of your Smart Cover-clad iPad mini. The case, available in colors to match Apple's Smart Cover lineup, protects just the back of your tablet.
When I say the CoverBuddy is slim, I mean it: The case is a decidedly svelte 1.5mm thick. It snaps onto the back of the iPad with minimal effort. The case has tiny holes around the iPad's speakers to allow sound out, and they worked well: I heard no impact on total volume output. There are also cutouts for the Lightning port, the rear camera, the side switch, top microphone, and headphone jack. The CoverBuddy uses press-through button overlays that cover the volume and sleep/wake controls; both work very well, with good "feel."
The case ships with four plug covers: two for the headphone jack, and two for the Lightning port. (There are two of each so that you have backups.) I'm not a fan of such port covers myself, but these fit snugly and worked fine. It also ships with an adhesive screen protector and a microfiber cloth. I'm also not a fan of those protectors--I prefer touching the screen directly, with no extra layer in the way--but this one seemed of the same quality as all the others I have encountered.
As designed, the CoverBuddy works beautifully with a Smart Cover: It covers everything the Smart Cover doesn't, and matches its look nicely. The rubbery texture is less slippery than the naked iPad mini's back and is comfortable in hand, and it doesn't detract much from the iPad's good looks.
If you like the Smart Cover but remain concerned about the lack of protection surrounding the rest of your iPad Mini, the CoverBuddy makes an excellent companion.