The sensor is the same as the Z6ii. It's not the stacked sensor being used on the Z9 and Z8. The processor is updated to match the Z9/Z8 - 10x faster than the Z6ii and better to support the AF modes of the Z8/Z9..
Of course, with the lack of the stacked sensor and dual readout, it's not going to have a real time EVF.
I think SD cards are a better fit for a casual photographer and a smaller image file. Even with a full buffer, it should shoot around 5 fps (UHS-II SD cards can write around 145 MB/s in Nikon cameras). But the buffer will fill pretty fast at 14 fps with an SD card.
The camera is not able to shoot fast enough and long enough for heat to be an issue. It is just 14 fps and a much smaller file than the Z8. That's a shooting rate less than 40% of the data being written by the same processor on the Z8. With the relatively slow write speed, the buffer will fill and it will slow the shooting rate. As a rule, SD cards tend to not overheat because of the write speed limitations.
Ricci's review is quite good as usual.