The older Grey tonearms sometimes show up on ebay, often on equally old tables. While apparently there are people who use them, I suspect that they are way too massy and high friction for most modern cartridges, so I imagine they are either going to collectors who won't actually use them, or to whatever the audio version of Civil War reenactors is.
The MicroTrak is more plausible for use, but it lacks most of the consumer amenities such as tracking force guage, antiskate, cuing etc., and it looks kind of basic, even agricultural, so I don't think it appealed much to the general consumer, especially since in the seventies, even the best tonearms didn't cost all that much. (Well, maybe the Win and Stax did, but the SME was pretty affordable, as were most others).
I would think one might be a good stopgap on the way to a better arm, but I wouldn't pay very much. (Though its possible that with a better cartridge than the Pickerings my college radio station used, the result might be good -- I can't comment, since I never tried anything else -- I was just a DJ, not staff.)
