@lewm,
Straight underhung arms still skate, one way or the other depending on where they are on the record. The only arms that do not skate are straight tangential trackers. The problem is there are currently no straight line trackers that do not have substantial issues.
The fact that the Viv are sounds satisfactory to many people is an enigma as the distortion is substantial. Maybe we are not sensitive to that type of distortion. I applaud you for your curiosity and willingness to spend money on a device that might not work out. It is how you learn.