Downsides of open back headphones
The open back headphones are mainly used for mixing or referencing tracks in post-production sessions. They leak the sound out of them, and that can be annoying if you're using them in a coworking environment or in your home studio that is also a living room for your family. It goes the other way too. Any noise from the environment will get into the headphone unless you have them at higher volumes to mask it, which is not a great idea as it can hurt your ears. Studies show that at about 80dB you can only listen up to 9 minutes without hurting your ears and going into ear fatiguing moments.
But that being said, the mixing experience on headphones can only come close to standard monitoring situations with open back headphones.
OLLO Audio S4 are designed especially for mixing engineers
There's a lot of open back consumer headphones but not much in the mixing - pro audio area. One of the most popular is the Sennheiser HD650. If you're really into mixing on headphones due to necessity or you learned that it's possible to do great mixes and directing all your effects on them, then I'd recommend going with the S4 mixing headphones. They are designed for mixing engineers. The comfort will enable you to mix for 5 hours straight. The frequency response is designed to be flat out of the box so no need for any software correction. Also, the acoustics design of S4 was developed in a way to support minimal changes in SPL. So you'll hear a 1-2dB compression instantly.
OLLO Audio S4 vs. S4R
In comparison to S4, the S4R get a bit louder due to closed back design before distorting, and their frequency response is less flat. That comes with any closed back headphones. Due to the closed cabinet, there will be a resonance frequency that will boost as some spectrum range and dip right after it. In S4R that the 500Hz area. You'll find this to be at different spectrum ranges for different headphones. You can see the difference in the graph below.