BitRocket is a native BitTorrent client for the Mac. It is a very simple application that can be used to download the content of .torrent files. It was designed to use the libtorrent library, which is said to be powerful and versatile. There aren't many details about this app on its website and I couldn't find much on the web, so I will go with what I see.
In terms of design, BitRocket is extremely simple. It has a very to-the-point interface with big buttons and clear interface elements. The middle of the screen is where your torrents will be loaded and where information about them will be shown. Like other clients, you will see how many peers and seeds you are connected to, the download and upload speeds, etc. At the bottom of the screen, you can access extra information like progress, files, peers, etc.
In terms of performance, BitRocket seemed to do a good job of connecting to torrents of different trackers. It took it a few minutes to pick up speed, but once it did, it was fast all throughout the download. I can't compare it with other BitTorrent clients because I didn't do any exhaustive testing. But it seems to work fine.
All in all, BitRocket is yet another BitTorrent client. If you are happy with the client you currently use, I see no reason to make the switch yet, mainly because BitRocket doesn't have any spectacular features. But it does work well.