Short review of the Quartet and my full review is on YouTube (listed below).
It is a nice resin build. Comfort was good, fit was a bit tricky for my ears. The nozzle is shorter so I believe that is why I had issues. I ended up using a different size tip for each ear for proper seal.
Sound wise, here are the 4 options:
Both switches off (default tuning I'm guessing) will give you a good amount of bass. It extends very well. Midrange feels flat and you get a slight elevation of treble. Mids are a bit...muffled at times, but still give enough presence.
Both switches on: this is a more vshaped sound. Boosted bass and boosted upper regions of the FR. Great sound for casual, engaged, gaming and movie watching!
Left on and right off: this is my least favorite. Boosted bass but the rest is more flat. Gives to a dark tuning that is also warm up top. Perhaps useful for monitoring low end of music.
Left off and right on: this is probably more of a harman type tuning to me. Gives good bass still but then slightly boosts upper to give more presence. Great for vocals but also found good for natural instruments and classical arrangements.
Over all, I think the Quartet can have a switch tuning for everyone to enjoy. These can get bright to some, however, I did not feel they were for me.