Octave mando is a great horn for this style of music. We get nearly the range of the guitar (missing the bottom 3 notes E F F# only) with the great logic and symettry of the fifths tuning.
For those who haven't tried one, I urge you to check them out. As with guitars, there is a range of quality and prices, from entry level stuff (the Saga Trinity College) to fine handmade instruments such as those made by Bob Abrahms (Portsmouth NH) and Stefan Sobell (England).
I've never heard Django play a note without commitment.