I use CoreELEC installed on a SSD hard drive. It works impressively well, with 8GB permanent timeshift to watch TV and all tvheadend buffers increased 10 times. I have no problem, the device is flying at full speed.
I just have to comment on a peculiarity, the installation of CoreELEC generates a defective system partition that I always analyze and repair with Ubuntu ‘gparted’ (warning type: number of heads and cylinders does not match the hardware). This also happens with USB flash drives and microSD.