Despite no information given here, decided to get the Tt v21 case, and build with an asrock z270m extreme4 7700k.
I used 2x 200mm radiators, one front, one top. 200mm stock front fan, and 180mm Silverstone fan on top. I had to drill some holes in the fan brackets to place the radiator where I wanted, and space it with a 20mm shroud.
This case does not show compatibility with 180mm fans, but it supports one on top with mobo horizontal. There are four places that it will fit. Here is one example.
There was just enough space to install a primochill car d5 reservoir between the front radiator and mobo tray.
I had to modify the front io bracket and tip of one of the top fan brackets to move the io to the top and rotate the front panel.
I assume that this may be one reason why 180mm fan compatibility may not be listed. This issue is only there when bracket is in the 180 fan slot and io on top.
GPU is a tight fit, but clears radiator fan perfectly. 200mm fan will not work here.
The finished build is simple, and clean. A lot of tweaking went into the build, and there are a few times that I felt that thermaltake may have had a few different ideas for the case in development, but may have changed them as they came to release. Notably with the 180 fan compatibility, and what looks like a 5.25 bay slot in front (although that could just be for 240 radiator tubing).
Overall very satisfied with the case. Perfect size, great adaptability, and good watercooling compatibility despite not stating compatibility with 200mm radiators.
A couple things that I would have liked, more mounting positions for the fan brackets. Especially on the sides. I am planning to modify the case to install fans close to the motherboard tray to cool the gpu... like so
Then add a shroud to the top to compartmentalize the GPU air intake, while installing 92mm fans above the GPU to exhaust some of the heat since the cards location next to the radiator almost gives it its own compartment. I plan to keep the GPU on air for now, since I will be swapping a few different cards to bench them.
I had an nzxt rogue case before, which had some similarities in concept with this case. Flat mobo tray, side 120 fans blowing onto the gpu directly. There were limitations with the rogue, but overall the v21 has very few negative points. My biggest complaint is no 5.25 bay (for temp controller), but that would be problematic with the concept of the rotating front panel.
I had a blast building in it, and the versatility is a huge plus. Being able to rotate the case and swap the panels around is great. I am glad that I went with this case, I feel that the x2 would have been too large for what I wanted. Cable management feels like either an afterthought, or no thought at all... but with some work, they can be hidden enough to stay out of sight and out of the airflow.
Kudos to Tt for a nice cube design that's not too large or too small.