I've been using it for about a month now. Currently fed by an SMSL SU-8 in balanced mode, driving Beyerdynamic T1.2 via the balanced XLR.
So far, it's been really good and I'm able to push the T1.2s adequately. Compared to my Cavalli Liquid Spark, it actually sounds much more neutral with the stock tubes burned in, whereas the LS has a lower-mid hump, making it sound warmer some how. Differences in dynamics and resolution are moot, however the TA-20 has wider and deeper stage.
Didn't really understand how an amp could be 'holographic', but the TA-20 does sound more 3D compared to the LS. Maybe it's the depth and instrument seperation? As for speed, it's not noticeably slower, but maybe the T1.2s mask this, as they are fairly fast cans to begin with.
I'm really looking forward to tube rolling at some point, and I haven't pushed any planars with it yet, but overall I'm really happy with the TA-20. Not only does it sound really good, but it's pretty compact, has decent connectivity, is built fairly well and the price is quite reasonable. The fact that it's balanced end to end is a bonus.