sounds like a good cd. i have the sabar cd by the same producers (with mapathe diop) and also their bougarabou cd (saikouba badji) and those are great. tabala music is not as polyrhythmic though, probably due to its roots in qadriyya, a sufi sect from the middle east...hence a more middle eastern melange on african drums.
i don't know about the metal rings making it non-traditional. djembes didn't used to have the metal rings either... bougarabous used to be peg tuned like the sabar. but they are still traditional drums...tradition is not static but very much an organic thing.
there is a limit to what people will accept though. for instance, lug-tuned djembes are generally not accepted as djembes. neither will ones made from fibreglass or particle wood. as wood gets scarcer, people get busier and the technology improves, perhaps some of those things will become widely accepted many years from now.
