Unfortunately, it seems that B vitamins do not 'synergize' with caffeine in an appreciable way, per an article from the LA times in 2008. Caffeine does have a 'negative' effect on circulating B vitamin percentage, but I could only find one study from 2008 about it, and it's not unhealthy. As is, the B vitamins with coffee really only seem to help in the elderly.

That said, yeah, mate is pretty mild in terms of caffeine content.

http://www.latimes.com/health/la-he-skeptic14-2008jul14-stor...