I used their repos for a month or so on my Arch installation, didn’t have any issues and all my games ran the same but with no performance gain as I would have thought. “cachy-nvidia’“ is the same as the “nvidia” package on Arch/EndeavourOS, it’s the module needed to make the nvidia driver work for the linux kernel package. You could can also nvidia-dkms (or nvidia-dkms-open) which works all the kernel you install.
python-cachy is also a package in the Arch Linux repos and it’s not a package specific to CachyOS.
They also have their own customized proton version, which is fine since there ore more customized proton versions around.
Most of the cachyos packages you are talking about are either pre-compiled kernels with specific kernel modules and for several different architectures in different repos.
I do for people that want to use Arch without it being minimal like EndeavourOS and provides some extra graphical tools. However I thought I would have gotten a performance gain which optimized packages which wasn’t the case. Could still be that other people with lower spec hardware do.