My experience is that at first it was very frustrating. I went from ~80WPM on my macbook keyboard to ~20WPM on the ergodox. After a couple of weeks I was able to write text at a comfortable speed again, but any special character was painfully slow, as I had to consciously think where each character was, and often look it up on my layout. After about 3 months I was back up to 80WPM.
What took a long time as well, was configuring my layout to fit my programming needs, it took me about 6 months to come up with a layout that had everything I needed (you can see it here if you're curious[1]). My recommendation is to do it incrementally, trying with something general at first, then with use seeing what feels right and doesn't.
In the end it was a really good idea, a lot of back pain I had has gone away, and after long typing session I have way less pain in my wrists and hands.
[1]: https://configure.zsa.io/ergodox-ez/layouts/BOLz0/ybXMx/0