Experience With Linear Tracking Turntables

I owned the original Souther Linear Arm in the80’s & in fact went to Lou’s house in MA & saw his whole set up. It first was on a VPI & then a Sota  Sapphire. It could sound very good but setting & aligning it were a real pain as anyone one change affected every other parameter! 
 

Clearaudio bought his patents years ago & I believe still offer a pricey version of the arm.

i opted to go for a Basis w/ an SME arm which has since been replaced by a Basis arm many years ago now. It still sounds excellent w/ a good record & while different than my digital stuff( Innuos/ Bricasti), is equally enjoyable. 

There is a good argument for high effective mass in the horizontal plane. Bass frequencies predominantly elicit horizontal movement of the cantilever. If the tonearm has low effective mass in the horizontal plane, it is conceivable this would cause sufficiently high SPLs of bass to displace the pivot from side to side. So you might want high effective horizontal mass to avoid a situation where the tail (the cantilever) wags the dog (the pivot).  Several Japanese manufacturers must think this is sound reasoning, because several Japanese pivoted tonearms employ devices to increase horizontal effective mass.  Those outriggers you see on Moerch tonearms are a case in point (even though Moerch is not Japanese).  The Dynavector tonearms that not only have high horizontal effective mass but also use magnetic damping at the pivot in the the horizontal plane, are a Japanese example.

Increasing horizontal inertia is also the rationale behind the addition of using those little troughs of silicone fluid mounted with a small paddle attached to the tonearm  first pioneered, I believe, by SME.  I have one each on my SME Series II and Series III arms for my HW19, and added an aftermarket one from KAB on my SL1200GAE.  They do clean up bass response which can be measured and demonstrated during set up.  Some people leave them dry not understanding their purpose.