Pros: Sound quality, isolation, price?
Bought new in Europe for $100
My best IEMs, very good analytic sounding, obviously not for bass-head even though my favorite headphones are Denon D2000!
High isolation but might be uncomfortable (it goes deep in ear canal)
I had RE-0 as well, to me HF5 are much better, they are not bass anemic like Hifiman's
I still do not know how to evaluate the price, they are MANY newcomers in the market such as JVC FX series or VSonic which can be bought for less than $100.
If you need very strong isolation, don't look elsewhere!