Shimano/third-party rotor compatibility with low end hydraulic brakes 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&amp;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?
As you mention SM-RT54 and 66 rotors, I will infer you have Deore level calipers. (Deore is not 'low end' IMHO, as the 'cheap A's' (Alivio, Acera and Altus) and almost unmentionable Tourney are below it.)

If you check out the Shimano Product Line docs for Deore you will see that the SM-RT64, SM-RT54, SM-RT66 and SM-RT56 rotors are all compatible with the BR-M6000 and BR-MT500 calipers. The SM-RT64 and SM-RT66 are both metal pad compatible.

Note that the BR-MT500 caliper is not metal pad compatible though, so you should check your caliper compatibility.