See the wiki page for diagrams explaining the mapping.
The Electrix Tweaker is a flexible, well-built MIDI controller. It does not take up space with space with jog wheels; instead, there are a plethora of multicolor backlit buttons, 8 velocity-sensitive buttons, and 6 infinitely rotating encoders surrounded by LED rings (rather than finite range EQ knobs). It can be used by itself to control most aspects of Mixxx. It has no audio interface, so it requires a separate sound card (although it does include 5-pin MIDI in and out ports). It apparently did not sell well considering how little information there is about it online. It initially sold for $400 in 2013 but is now available for $100 with a free case and free shipping from the manufacturer.
The flexibility of the encoders with LED rings and the multicolor buttons allows this mapping to fit a lot of functionality into a small package. The encoders control EQs, gains, loops, and coarse seeking in various modes. This mapping can control 4 decks by toggling between decks 1/3 on the left and decks 2/4 on the right. Each deck shows 8 hotcues at a time and 4 pages of hotcues are available, providing access to all 32 hotcues allowed by the Mixxx engine. This mapping also takes advantage of slip mode, which is not yet available through any of Mixxx’s skins. With slip mode and all those hotcues, this mapping is excellent for cue juggling.
The Tweaker is a USB MIDI class compliant device, so it does not require any special drivers on any operating system. Just plug it in and load the Mixxx mapping on any OS that Mixxx runs on.
The latest mapping is included in Mixxx 2.0 RC. Use it with the Tweaker MIDI 1 port (Tweaker MIDI 2 is the 5-pin MIDI I/O on the Tweaker).