If you enjoy building a kit and have the ability to build your own boxes then going the kit route will give you more for your money every time.
The OB-7 has a few performance advantages in that the use of the open baffle gives you a more open and airy presentation, especially through the vocal region. It's use of multiple drivers also lowers distortion and allows for greater output levels (91 db sensitivity compared to 86 or so with the Mini). The OB-7 also uses a larger 12" powered woofer. It has a much great power handling ability too. I'd clearly have to give the overall performance edge to the OB-7.
However, the Mini does nothing wrong and everything well and does so for a very good turn key price that makes it tough to beat. No fully assembled speaker in its price range is going to touch it. The planar magnetic drivers give it resolution and detail levels that easily match the OB-7. It looks beautiful too.
It just really depends on what you're looking for and the price range that you are looking in as to which route you might favor.
