The mighty ET2 was left out of that exclusive club. Never owned the Triplanar, but have owned the SME5 and the Graham and still own the ET2. In the ways that matter to me, and with the many cartridges of both the MC and MM variety that I have used, the ET2 comes out on top. Still available and still beats the SME5.
I used to run a Rabco that I modified. I get the allure of straight tracking.
I left the ET2 out on several counts. The first being that the lateral tracking mass is a multiple of its vertical tracking mass. This makes selecting a cartridge rather difficult- if you succeed in getting the mechanical resonance correct in the vertical mode, you’ll see the cantilever bending back and forth on occasion. When it does that, due to the short radius of a cartridge cantilever, the tracking angle error is higher than any radial tracking arm.
Second, it uses an air bearing. If you want the cartridge to play without coloration, there can be no play between the surface of the platter and the mount of the cartridge. We know that bearing play makes a difference since you can use higher pressure pumps and hear a difference.
Finally the arm mass is high enough that a decision was made to run only 4 wires rather than the traditional 5. Cartridges are balanced sources and they don’t make a lot of voltage. When the arm ground is integrated into the left channel signal, it can be noisier. Plus you can’t run it balanced should you wish to do so; something you can do with most arms. One result of this can be RFI, although use of RF beads can sometimes sort this out.
So IMO it didn’t rate the top drawer.