I trained in capoeira for a couple years at the ABADA school in New York under Mestre Bom Jesus. It's "regionale," the combat style of capoeira, as opposed to the dance style (angola).
I definitely agree it's a ridiculous workout, and anyone who trains in capoeira is going to develop excellent cardio. There's just no other martial art that demands such constant movement and places such an emphasis on escapes. It's not possible to "play" capoeira and remain stationary, and the formal sparring style demands combinations and improvisation.
But...at the same time, I'd just caution that you do a ginga in a match, you're gonna get your ass beat. It goes deeper than that, of course, but we're talking about a style with no blocks and no handstrikes whatsoever outside of taboo eye gauges. Some of the kicks are amazing, and the most basic ones are the same as other martial arts, but there are also an assload of impractical kicks and sweeps. And those esquivas (escapes) would leave you open to getting stomped or kicked in the head.
So I like capoeira as a workout, but I do think it could lead to some bad habits for anyone who would think about incorporating it into an MMA repertoire.