I'm maintaining a gallery of split mechanical keyboards, including the Ultimate Hacking Keyboard. Hopefully it's helpful for a quick overview of the options that exist. Many of these keyboards are DIY (available as a kit, or sometimes just a PCB and case plan), but some are available assembled. https://aposymbiont.github.io/split-keyboards/ (There's also https://jhelvy.shinyapps.io/splitkbcompare/ for direct comparis…
It's kind of you to compile this list. Please add this very good product: https://www.goldtouch.com/ergonomic-keyboards/ I am a very satisfied user. I have used ergonomic keyboards for long time. Some have been passable, such as one or two models of Adesso and Microsoft keyboard. Nothing has offered the combination of qualities that the Goldtouch offers. Comfort, robustness, adjustability, cost.
I have added a link at the very end to one such site, http://xahlee.info/kbd/ergonomic_keyboards_index.html , where the Goldtouch is listed and reviewed.