The mentor and merlin are 2 very different beats.
The merlin follows that typical v shaped fun sound with emphasized bass and treble sparkle. Think m100 Sig but much much more refined.
They are a stereotypical fun sounding iems.
The mentor isn't going to hit you in the face with this fun sound that will knock your socks off. They aren't neutral but they have less emphasis on any particular part of the spectrum than the Merlin's.
The mentors are thick sounding with lush mids and plenty of bass but also have amazing detail and treble extension.
I would rate the mentors well above the Merlin's, but if it is that v shaped sparkly bassy sound you want with mids that are either recessed or seem so due to the fr, then go the Merlin's
Didn't help? Sorry ha ha. If I could I would just own both.