You are right that for the same power the current draw will be far less at 230V than it is at 12V. I was unaware you could get heat beds that ran on 120V or 240V. The ones that run on 120V or 240V likely use resistance wire; suggested by the wirewound reference in the resistance description. From a thermal standpoint it should work. Most of us would just prefer to deal with low voltage at a higher current than mains voltage at a lower current.