I've had both ZS10 and T2 for quite some time, there's my two cents:
- bass is deeper and stronger on ZS10, they're not bass cannons but have a thick low end rumble, while the T2 don't have too much bass oomph unless you cover the vents. Both have good bass quality, but ZS10 is a step ahead in quantity and two ahead in depth and sub-bass rumble.
- mids are way more present in the T2, they're not forward but just "natural", bright, maybe a bit cold for my taste, but they make vocals sound realistic and preserving the timbre. ZS10 have subdued mids, making vocals sound a bit distant, sometimes male vocals a bit cold too, but they're good for relaxed listening sessions. Both have no sibilance at all, maybe ZS10 are even less fatiguing in the midrange, but both are ok.
- highs are completely different on both. T2 have some more treble presence giving them some extra brightness, but they're not fatiguing or piercing. ZS10 have a peak in the lower highs (around 2kHz) that might be too much for some listeners, but at the same time upper highs are very present but not exaggerated by any means, making them one of the most detailed IEMs (if not the most) I've heard so far.
- soundstage is better on ZS10 but not by a long shot, they don't have the huge soundstage that ZS5 v1 had. Instrument separation is where the ZS10 excel, they're a serious step up in clarity over anything I've heard so far, I guess the 5 driver setup has something to do with that. T2 have average soundstage and good detail tho, they're not bad by any means, but ZS10 plays on a different league here.
- comfort & fit are a hit or miss on both. T2 have big round housings with short & 6mm wide nozzles, making insertion and getting a good seal seal a bit challenging (I had to use extra wide XL tips, usually using L size). Also the T2 shape is not the best, you have to insert them slightly angled because of the straight nozzle, so they might be not too comfortable after a while. ZS10 have greatly shaped curvy housings with short-ish 5mm wide nozzles (not like the sharp ZS5 & ZS6, thank god!) but they're MASSIVE (really, check out the next picture so you can see how big they are compared to the not-so-small T2 and the relatively tiny Swing IE800). If your ears are small, ZS10 won't fit, that's for sure. My average ears can barely accommodate the ZS10 housings, but once they're in they stay (memory foam tips help too), but they noticeably protude and are no good for lying on your side or anything like (they're not good bed buds). I'd give ZS10 the advantage here because they seal me better and they're almost unnoticeable once I manage to get them in.
- build quality is good on the ZS10 and excellent on the T2, good news is both have detachable cables. ZS10 have good quality plastic housings and a nice braided 2-pin 0.75mm brown cable (a huge upgrade over previous KZ included cables), but also include the same cheap KZ tips (get better ones asap, preferably memory foam). T2 aluminium housings are top notch, and the included memory foam tips too, but my silver braided MMCX cable got a green-ish tint after a few weeks of listening, and it was getting worse, so I bought a replacement for ~$7 it and never looked back.
- to sum up, I'd say both are great in a different way: T2 excel at midrange presence and natural tonal balance & timbre, while ZS10 offer excellent instrument separation, great detail, and good bass. If I could only get one, I'd get the ZS10, because if I want a natural sound I go for over-ear open-back headphones (and even when I can't, I prefer the sound and comfort of the ZS10 over the T2).
Tin Audio T2 (left), Swing IE800 (center), KZ ZS10 (right). Both T2 and ZS10 have upgraded cable & tips, fun fact: my T2 upgraded cable is made by KZ.
Stock ZS10 cable (top) and T2 cable (bottom). Notice the green-ish tint on the T2 cable, looks like some kind of rust was happening so I replaced it (also got rubberized memory wire on the ear section, better comfort).