Having owned the U12t for about 6 months prior to the announcement of the Nio, I can say that it's great and is very relevant still. The treble on the U12t is definitely more present and effortless compared to the Nio. At my usual listening level, the U12t is definitely the more balanced of the two (even without taking the bass into consideration) and detail retrieval is a bit better too. From memory, I think I still prefer the U12t for metal, just because of the speed and accuracy of the lower frequencies. You get a bit of bass bleed with the M15 module and the level of bass isn't enough for my tastes with the MX, so you need something in between. The Fir module O is a
must have in my opinion, as it reduces the bass just enough to balance things out.
As
@Mrcojocaru said previously, the Nio is very similar to the VE8, especially in the mids. They're right in the center, and you can hear them well. From memory, I'd say the vocals sound very similar and there's very good weight / emotion to them. For some reason, I don't find the Nio to be as thick sounding in the lower mids, especially with the MX module. The bass is probably a bit more controlled on the VE8, but it's obviously more impactful and realistic on the Nio. The VE8 hisses with almost everything and the sound changes a lot depending on the OI of your source, so that can be a negative for some.
Finally, there's the Andro 2020. Like I mentioned in a previous post, I would recommend it over the Nio if you're a low volume listener and you want the absolute best bang for your buck in the TOTL realm. If you NEED a DD for the lower frequencies and listen fairly loudly (around the 80 dB or more), then the Nio is a no brainer. Even after A/Bing against the Z1R, I felt like the bass wasn't very far behind (the Z1R has a more effortless bass). The only thing you're missing out on is the treble sparkle and maybe layering of the Andros. If you guys ever get the chance to try those two side by side, please let us know your thoughts !