An ergonomic split keyboard. Suddenly I can type without rotating my shoulders inward. Which in turn means more room in my chest for my lungs to expand. The difference was not subtle. Learning to touch-type on this thing took a while but was totally worth it.
I don't really have ergo problems like other people though, and a regular 10 key Filco Majestouch 2 is my daily driver now. But I did like the Freestyle when I used it. It's worthwhile to get the angular stand kit that is an addon when you buy it (I believe it cost an extra $30 USD or so when I got it, but that was years ago)