THE Mercedes-Benz M-class is a rarity in its class because it performs well on or off-road. It is also a realistic proposition as a day-to-day conveyance with most of the carrying ability of a big 4WD, apart from having only five seats, and none of the dynamic hang-ups. The finish is close to but not quite up to the Mercedes sedans. Its entry level pricing looks pretty attractive against Range Rover or LandCruiser/Lexus and, of course, it offers the traditional levels of safety and snob appeal.