Lewm - As to the problems, everything of a technical nature has its pluses and minuses. So for a linear tracking tonearm, the problem is to drive the tonearm and cartridge across the LP surface, some sort of for force is required. That can be in some cases a servo motor, in some cases gravity, and in some cases just an attempt at zero friction back at the pivot point.
Huh?
The best linear tracker tonearms use the same force for movement as a pivot arm - the groove.
But they do not need antiskating and the cart does not sit at an offset.
Have you ever actually owned and used a linear tracker in your room, Lewm ?
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Uberwaltz - I believe you are referring to the packaged deal TT setups that included a table, tonearm, cart and available for reasonable amounts? Something like the Technics SL10 I have kicking around in a closet somewhere.