They have it customized, they have also btrfs integrated with md, which is not in the stock kernel, but these are runtime things. Not to say there are not a way

They have it customized, they have also btrfs integrated with md, which is not in the stock kernel, but these are runtime things. Not to say there are not a ways to shoot yourself in the foot (e.g. being careful when creating ext4 volume with external machine, target nas might have older kernel that doesn't support half of the newer ext4 features and 64 bits). I never had any problem with thermals or psu, but I've heard other people had psu problems.