Linear Tracking Turntables - Best??

The much higher effective mass in the horizontal plane of most linear tracking arms might not necessarily be a disadvantage.  Bass is typically mastered monophonically, which means only lateral movement of the stylus tracing the groove.  The higher effective mass in the horizontal plane would keep the arm from moving so easily so that all of that bass information is imparted to moving the cantilever which means that all of the bass information is actually recovered by the cartridge.  This is the principle behind the Moerch anisotrophic tonearm.  I don't know if this is also what is behind the sound of certain linear arms, but, it might be the case.  With arms like the Walker and Mapenoll, I heard really deep and powerful bass.  

Of course the higher horizontal effective mass would be bad news with off-center records which could severely stress the cantilever.

Does anyone have experience with the Shroeder linear tracking arm?    

The air bearing "slop" issue has to do with not having physical contact between the arm and the structure of the rest of the table (arm base and plinth).  Micro vibrations caused by the stylus tracing the groove don't have as effective a path to be dissipated elsewhere so the arm itself tends to shake.  That energy can be damped and reduced by a "stiffer" air bearing, but, this is just one of the challenges of designing air bearing arms.  

As for the mass issue, it is not just that these arms tend to have higher effective horizontal mass, it is also the case that the stylus/cantilever has to drag the whole arm from the force applied to the end of the arm without the mechanical advantage that pivoted arms have (pivoted arms are effectively levers).  My other issue with most of these arms has to do with their shortness.  The shorter arm has certain advantages (lower vertical mass, greater rigidity), but it also means greater changes in VTA from different thicknesses of records; both of my cartridges are pretty sensitive to small changes in VTA and I am not someone inclined to fiddle with adjustments for each record.

Whether or not the inherent mechanical challenges of such arms outweigh the advantages, is, I suppose, a matter of debate.  I do know that I have heard some pretty nice sound from systems using air bearings like the ET 2, Walker, Kuzma and a few others.  I even liked the sound of my cheapie Mapenoll but I got rid of it because of the issue of the cheap air pump not delivering enough pressure.  But, I have also heard terrific pivoted arms of all sorts, so I am not convinced of the inherent superiority of any particular design.