I recently bought and Ergodox-EZ, after previously getting my first mechanical keyboard (the Ultimate Hacking Keyboard, which I love).
I'm not a huge fan of it. So far, it seems like it's been a lot of work relearning habits, for little gain.
But oddly enough, my biggest gripe with the Ergodox isn't something I've heard people complain about - the lack of an extra column of keys on the right part. Basically, on a normal keyboard, to the right of the "l" key, you've got another 3 keys - a ;, a ', and the enter key. They're all pretty important.
But on the Ergodox, you only have 2 more keys. Meaning you either have to move the return key to somewhere else, or move the "'" key somewhere else. Both of them break tons of muscle memory, and for no real benefit IMO.
In addition, the lack of that extra column means that symbols like [], like -=, etc can't be in their regular locations. Obviously, as a programmer, these are all keys I use a lot.
I don't know that much about mechanical keyboards, but I really don't get why this choice was made. It seems like a completely self-own here, making it so much harder to get used to this keyboard.