Man those red M50x were my first entry into the headphone world. Personally I just never found them comfortable enough to wear long term and mine were the older model I guess without the removeable cable so they were kind of a pain to go around with. Ended up getting rid of them fairly quickly but I really appreciated the build quality. The plastics felt really really solid.

My next pair were the discontinued and absolute trash HiFiman HE-300. These things were such trash. I bought them with some bundled amp that was also terrible. Really really bad headphones. Uncomfortable, poor quality, terrible cable, sounded bad. I'm now temped by the HE-400SE but I'm still doubting the build quality and other concerns.