I also have the Sony PSX-800 with linear tracking biotracer arm, and find that it performs flawlessly. For example, it will play records so badly warped that an ordinary arm gets tossed completely out of the groove.
The reason that I bought it was because I attended a seminar at a High End audio shop on the subject of how to set up a conventional pivoting arm. I never realized how many angles and tracking forces were involved, and how many of these errors can only be approximately corrected because things change as the arm tracks the record from outside towards the spindle.
I think that most linear tracking arms failed because they relied on virtually frictionless bearings so that the arm would move with a very tiny sideways force from the stylus.
The Sony Biotracer arm uses servo motors to move the arm (side to side and up and down) so as to keep all those troublesome angles down to about 1/10 degree. Stylus downforce is also applied electronically, a nice feature which lets you adjust the force while a record is playing so that the sonic effect can be heard.
