If I had to compare it to any other tool, it'd be git. I love git. I use git every day. Do I understand the underlying mental model of git, or the 348 different git commands? Hell no.
Having said that, I'm also pretty sure that Om yields bigger payoffs further down the road as far as I can tell.
Beyond that, the new reg-effect-fx system isn't particularly mature, individual fx aren't extensible, e.g. being able to extend http-fx to cancel or debounce requests.
I don't _hate_ it, I'm building apps in it. I just think there's a lot of overhead above Reagent that I have yet to see pay off, and the idea that it _forces_ best practises is wrong. It's like an MVC system that lets you put (_encourages_ you to, if you read the docs) controller code anywhere.
It's likely that I'm just too dumb for modern web programming, but I am waiting for someone to distill the (admittedly brilliant) ideas behind Om into something just as powerful but more usable. Reagent is elegant and simple, but you can see how it falls down in the face of larger apps, re-frame I just find a mess. I'm excited about all of this, but I don't think we're really there yet.