Shimano say that their lower end hydraulic brakes (e.g., BR-M365) are compatible with 'wide' rotors. See http://productinfo.shimano.com/#/com/2.0?acid=C-461&cid=C-460 for details.
Wide rotors are those numbered below 60, e.g., RT54. Narrow are those higher than 60, e.g., RT66.
The wide rotors (i.e. those below RT60) are made of low-quality metal and claim to be incompatible with metal pads.
What are some third-party, etc. options for getting better quality rotors?