A Master Fader is just a way to adjust the level of one of the "n x 2" mixer pair outputs - every "n x 2" mixer has this capability. Summing all inputs in the same mixer (for instance routing all tracks to output 1-2) is theoretically better than having several sub-mixes (like 6 tracks mixed to bus 1-2, 6 to bus 3-4, and 6 to bus 5-6, then all of them mixed thru Aux inputs to output 1-2, since the summed bus will only be dithered to 24 bits once (instead of 3 times for the bus mixers, and then 1 more time at the output 1-2 mixer). But, the difference is small - and must be weighed against the convenience of using sub-mixes (you could try using groups for doing "group-wide" level adjustments).