I've noticed that when I click on the blue "i" icon for more information on a character in the iOS app, one of the fields shown is the level.

Where is this level coming from and what does it relate to? Is it the frequency of this character? How long it takes people to master it?

Didn't find anything about this in the in-app help.

It's basically standard usage frequency mixed with relevance in learner-focused textbooks (so that you don't get 经济 as more important than 你好). It should be thought of roughly as a measure of importance, although the names seem to sound like they imply difficulty. That's something we haven't worked into it yet.

Does it affect how things are weighted in the SRS? Are more frequent items drilled more aggressively, for example?

Nope. It's more for you to look and see, "Hmm, this one is "hardest"-- probably not worth learning. I will ban it." or "Do I need to know this? "medium": yeah, it's pretty common."

Ah, I see. Thank you!