In T11_fan's guide, it's 3-6-1 Butterfly, and in the 2.0 Guide, it's 3-2-2-2-1 Butterfly, which I think is meant to be the same formation. The second form gives me a better idea.
Are we talking two DMC, two MC and two AMC?
I have seen this formation and thought it was very ugly. I don't remember how I did against it, it is possible that it gave me some trouble.
I noticed that it is often listed as a counter to various formations, so guide authors must think it is a strong formation. It is listed as a counter against my next opponent's 3N-4-3. For once, I have personnel to try it. I rarely have such luxury as 2 DMC or 2 AMC on my mean and lean squad, but early in the season I am still trying people out.