Do I sell meters with few functions? No. I don't sell meters. Do I use meters with few functions? Yes. All the time. A clamp-on DC ammeter for tweaking the final amplifer of a Hewlett-Packard 606A; an AC voltmeter for measuring the characteristics of amplifiers and filters; 4-terminal ohmmeters for measuring the contact resistance of connectors and switches; digital capacitance meters for matching capacitors in value; frequency counters for accurately adjusting oscillators and signal generators for certain frequencies.
Generally speaking, single-function meters tend to me more accurate than multifunction meters. For example, the older differential voltmeters were DC-only and measured DC voltage very accurately, down to 0.001% or so. AC voltmeters had a wide range, say 1mV to 300v full-scale with a frequency response to 10MHz. 4-terminal ohmmeters could measure low values of resistance, far less than 0.1 ohm and do it very accurately, say to 0.1% or better as well as measure high resistances. A frequency counter can measure from 10 Hz to 18GHz with an accuracy of at least 0.0005%. A good digital capacitance meter can measure from 1pF to about 1F at an accuracy of around 0.5%. If you attempted to put all these measurement capabilities together in to a single meter, it would cost you at least $10,000 and you'd lose your portability in the process. Instead, manufacturers try to put these functions into something affordable, and to do so, compromise heavily: smaller capacitance ranges and not nearly as accurate; less-sensitive AC voltage measurements and not nearly the same bandwidth -- you're luck if you get over 100KHz; and it goes on and on.
The vehicle analogy was supposed to be similar: a farm tractor can pull extremely heavy loads slowly over very rough ground; the Freightliner road tractor can pull very heavy loads at high speeds over smooth roadways; the Corvette can't pull anything but itself, but can to so at even higher speeds on curvey roads. There is no one vehicle that could do all of those things, because once you have the farm tractor's tires installed, you've just killed speed and maneuverability. If you tried to keep things low to the ground like the Corvette, you could barely clear speed bumps, let alone large rocks. You just can't compromise some things. That's why we have medical specialists or 25 different types of hammers.
Generally speaking, the more expensive the meter, the higher the quality. But there's more to it than that. Better accuracy and precision demands a higher price. Better realiability demands a higher price. Name brand recognition results in a higher price. More features (not necessarily functions) demands a higher price: remote readout, printer capability, GPIB interface, plug-in capability, long warranties, upgraded specifications. All of those things go together to better the quality.