Yes, the headphones really represent polar opposites on the headphone lineup. Grado, provided the sound that captured my attention and drew me into the headphone scene. Then, there were the options such as wooden cups as well as other options came along to include the Magnum drivers. I was quite happy with the headphones and what Grado offered. Then, I started to go forward with trying out other brands and types of headphones. Along the line, came the HE-400s, and I was really taken in by their performance. But, the HE-400s do have more weight to them than a typical pair of Grados. However, if headphone size / weight do not seem to bother you, the HifiMAN should be highly considered. However, if one needs a more compact headphone with a bit less weight, one should consider some other brand or model.
However, I really love my HE-400s and they perform very well for my listening needs. I had a chance to move a pair of Grados in my lineup again a few months ago. But, I found that I could no longer reconnect with the sound offering of the Grados. I had become quite accustomed to the sound offered by HifiMAN, modified Fostex, Audio Technica (A900x) as well as others. While I am fond of Grado as that was the line that got me introduced to this hobby, I really don't have any immediate desires to have a pair of their headphones in my lineup for use.
It all depends on the person's preferences.