So the ~200 I spent on my custom Dactyl that has actually taken my pain from a level ~4 to near 0 is really a drop in the bucket for my health.
(+1 for the DM! I have the normal Dactyl because a thumb injury makes the cluster unusable for me, but I have plenty of friends who love the DM.)
For me, on the existing flat thumb ergos, hitting the thumb buttons with the side of the thumb actually feels normal to me in terms of thumb & wrist motion. The primary issue is the angles and arc of the splaying of the thumb to hit the keys without having to contort my thumbs any. This is my biggest issue with the Kinesis Advantage and ErgoDox.
The second biggest factor is that the tall Cherry style switches and keycaps requires a lot of travel distance for activation. One the more recent ergo boards, I've switched to lower profile switches and that makes a non-trivial improvement as well. My upcoming build is with the choc minis + low profile keycaps but with heavier springs so they feel more like the last generation of the 17" MBP keyboard (as opposed the crap that's Apple's done with their recent keys).
And I like that you can download templates so you can print them out and find the right size.
Having started with very generic ergonomic keyboards, and now progressing to hand built keyboards have taught me that if you are experiencing some sort of tendon, nerve, or joint issues from standard keyboard use, you really need to dive into the deep end and get the most ergonomic thing out there even if $300 for a keyboard, when you can buy one for under $20, sounds incredibly expensive. If you don't, you'll likely end up paying that much to just keep fixing or improving the situation. And if you don't try to fix the situation you'll pay for it in damage to your hands which to me has no monetary value* .
I might still choose to build the manuform, but it's nice that there's an option out there with adjustable thumb keys, I've never seen that before and I hope it becomes a trend in the split ergonomic keyboard world.
[1] https://tomoakley.me/article/2020/01/1-month-with-the-dactyl...
[2] https://blog.splitkb.com/blog/introducing-the-kyria
* okay, maybe there is an exact amount in terms of how much money you can no longer make through typing ability that is lost, but my point is there is an intrinsic value to having fully functional hands.