A lot of externals are configured to report back 4K physical / 4K logical sectors as a result they do not have the need to partition using GPT since they have 1/8 the sectors and that number can fit in a 32 bit integer.
Although with that said in either case I would still use a GPT partition. Disk manager should at least give you the option to create a GPT partition.
My second recommendation is to do a full format looking at the SMART data with CrystalDiskInfo after the format. You will be surprised how many drives are DOA.