I can chime in and say that I was one of the original guinea pigs for the Poseidon tube rolling experiment. Laszlo was goodly enough to set me up with a set up TP adapters for both ECC40 tubes and a set of 4654 tubes and I can report both as being a very nice step forward.
When I directly compared the ECC40 tubes with the Soviet-made Reflektor tubes, which my partner uses in his Poseidon, the differences were subtle. Initially, I was inclined to prefer the more expensive Reflektors, but after level matching the volume, the distinction became less pronounced. The ECC40s, using TP adapters, delivered better bass and overall solidity, while the Reflektors had slightly more top-end sparkle and air. Given that the Reflektors cost over $1,200, the TP adapters with ECC40 tubes offer exceptional value.
Regarding the 4654 tubes, my comparison was limited to the stock Chinese tubes that came with the system. While these stock tubes are quite competent, the 4654 tubes enhanced the music with greater density, heft, and dynamics while presenting more apparent detail. The TP-adapted 4654 tubes particularly complemented my system, making the music bolder and more dynamic.