While I only joke about my attraction to playing chromatic button accordion, my interest in the accordeon mixte system has been increasing. I would define the mixte system as having a bisonoric right hand (treble) and a unisonoric left hand (bass/chords). This could take many forms, including a standard 3-row layout for the treble with stradella basses.
Here's an example that I found on YouTube. (Are the bombarde and binou koz actually mic'd? Yikes!)
(Video on/from YouTube.)