Like pedal tones, there are various ways to free buzz. Reinhardt has one way which I haven't tried but doesn't look that tireing. Pops has a different approach which also doesn't look strenuous. Callet teached "spit buzzing" which is yet another form of free buzzing. Caruso used it for therapeutic value. Pocius uses it for beginners. Its really difficult to make generalizations about free buzzing. Pragmatism is the way to go.