The MiniStack is a cool product in that it physically matches the size of the Mac Mini. I use a Mini for something of a home server, and when the external drive that was attached died, I figured I'd make my desk look a little nicer with a matching drive, rather than another of the typically oddly-sized / shaped external drives.
It's way too early comment on things like durability, and I'm generally happy with the purchase—it's the same size, works well, seems to move data reasonably quickly for my purposes.
But there are two "buts": 1. Visually, the MiniStack is not a perfect match for the Mac. Size is perfect, but the color and texture of the metal is not quite right. The texture is not as beautifully smooth, and its silver is more "metallic" than the Mini's body. 2. The product description uses the words "whisper-quiet." That's perhaps technically accurate—whispers are pretty quiet, after all, but the drive is noticeably louder than the previous external drive was—even before it died. ;)
I could go whole hog on the overly-detail-oriented thing like some Mac users do, and cry about how the LED isn't "elegant" enough or some such, but that'd be too much.
Overall, I'm happy. The drive is doing its job, and looks pretty good. This non-matching silver thing is common with lots of other peripherals, too. But in the photo on the product page, the MIniStack and Mini look a lot more similar, and if you're hyper-sensitive to "aesthetic Mac perfection" you may be disappointed.