I’m running an s912 box, a mecool m8s pro-L with the 9.2.4.1 firmware (non-ng) and it is working fine.
I also have an s905x3 box, and comparing cpu load between the two, the s912 box requires less % cpu for the same task.
For example, the Netflix addon is the most cpu intensive thing I’ve seen on it, and on the s912 it runs at 150% cpu for 8 cores (about 19% overall). Whereas the s905x3 box runs about 230% for 4 cores (about 58% overall). That’s 720p for both. Neither can do 1080p smoothly.
On the s912, the Netflix addon is the only thing I’ve seen use all 8 cores. When Kodi is playing a file, or the youtube addon is running, only 4 cores are utilized.
The mecool box runs hot, though. It got up to 80c with Netflix. Sitting on a notebook cooler, 64c.
This is legacy hardware. I got the s912 box about 2 years ago. There are better options today, but if you’ve got it, it’s still fine, I think.