I’m just reporting what a friend of mine told me after he spoke with Harry years ago regarding his VPI TNT Jr/ET arm. According to him, Harry told him the TNT Jr. was developed with the ET arm.
As you may know, The TNT Jr. had no sprung plinth like the Hw-19. Having said this, lots of people used the ET on the VPI HW-19 series w/ spring suspension as did I (initially), also a lot of SOTA users did as well. In my experience the ET needs a more stable platform to work the best. Just think about it... that long counterweight beam hanging on the end of the ET is subject to any movement times a lot more than a regular pivoted arm. Some refer to it as "the tail wagging the dog". This is why some of the later developed upgrades for the ET were the double or triple spring I-beams, to help stiffen the I-beam or to have less movement at the I-beam..
You said above, "I believe it competes with the finest today". In my experience, it’s not even close. I suppose it comes down to what one’s definition of "competes" is? Why would VPI remove the HW-19 series out of their line-up if they thought this way?