I got three in use currently, and I don't use other keyboard anymore. I think I have been using ErgoDox exclusively for more than two years?
Before ErgoDox, I never learned how to type properly. However, I can now type without looking down on the ErgoDox. It might be the separation of the two halves that helped keep my hand on their home position.
Also the TMK firmware helped, because I have assigned the arrow keys to my right hand home row. Thus I seldom move my hand away from the home row.
Portability is indeed an issue, that's why I got three in every where I might use the computer seriously. I also think a "compact single-piece symmetrical-stagger keyboard" is a good one. Not to replace my ErgoDox, but serve as a portable input device that I can carry around.
Interconnection was an issue, but I have overcome this with RJ11 cable, custom TRRS cable, dual mini USB cable, and they all work pretty well.
The thumb cluster could be improved, because I didn't use all the keys in the thumb cluster. But with enter, space, del, backspace and modifier keys in the thumb cluster, the advantage outweights the disadvantage.
I am really happy with my ErgoDox, and will remain so in the foreseeable future.