Unless the MDR-10 term is trademarked, how is it exploiting the law? The MDR-10 patents are expired, thus the subject matter that they claimed are in the public domain for anyone to use. Of course, that does not shield Hifiman's HE-R10 from criticisms of being a knock-off, copycat, being unoriginal, etc. Imagine the criticism when the sound quality of the HE-R10 is found out to be a step down from Sony's MDR-10. A lot of popcorn will be had then.
It's exploiting the reputation of another product from another company. For instance, if someone says in the future "The R10 is terrible", or "The R10 is great", what are they referring to? HE or MDR? If HE, then planar or dynamic?
The R10 (before Hifiman) was always classified as MDR, however it was colloquially referred to as R10. Now, Hifiman has essentially stolen this name to intentionally cause confusion. Hifiman has retroactively inserted themself in every R10 conversation, because as a follow up, we will ask HE-R10 or MDR-10. This is clever but rubs me the wrong way.