I just bought a ergonomic columnar keyboard (the ZSA Moonlander, to be specific). Since I knew that I would need to acclimate to the top and (especially) bottom row key locations anyway, I decided to go all-in and learn Colemak-DH at the same time. This will be a journal of that progress.
History
I've been touch typing on QWERTY for approximately 25 years using ANSI staggered keyboards. My speed in typing tests is an uninspiring 60-70wpm on normal English text with capitalization and punctuation but no numbers or symbols. My technique is very plain: no alternate fingerings to avoid common single finger bigrams; standard fingerings for every letter except 'C' (left index) and 'Q' (left ring); and exclusive use of the left shift.
Why Colemak-DH now?
Switching to a split columnar layout gives me a chance to imprint a new layout on the new board. I've long thought that I was a good candidate to see good results from a Colemak layout, because I have no personalized tricks compensating for its many weaknesses (ie. I'm completely unlike Sean Wrona). However, I've always balked at the risk of compromising my ability to quickly switch back to QWERTY when I need to use another person's machine, which comes up frequently but briefly in my day job. I'm hoping now to teach my fingers that laptop=QWERTY and moonlander=Colemak-DH. The Moonlander also allows me to leave the OS layout at ANSI-US, which cleanly by-passes any remote desktop issues.
I chose Colemak over Dvorak and Workman, because single finger bigrams are my top priority, and it's popular. I chose the 'DH' variant, because it seems perfect for a columnar keyboard.
Current Progress
I began dabbling in keybr about two weeks ago, but I stopped once I got to letter 'D', since I didn't want to mess with the bottom row until I received the Moonlander. When that arrived two days ago, I plowed ahead with the full layout. Current speeds on the default simple settings of Monkeytype have me at around 30wpm and 90-95% accuracy. My "real" speed when composing, however, is dramatically slower.
I'll add more thoughts latter. This was all typed in Colemak-DH, so I'm pretty exhausted at the moment!
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Update (2022-02-22): It took me approximately 2 to 2.5 months to gain speed in Colemak more or less equal to my best QWERTY speeds.
I have stuck with my initial plan to use Colemak-DH exclusively on the Moonlander and use QWERTY exclusively on all row staggered keyboards. I have been surprised by how little I've used a row stagger keyboard. Basically, I have only been forced to use QWERTY when interacting with other people's computers (which is fairly frequent but always extremely brief). As a result, my ability to do my normal work on QWERTY is probably extremely hampered at this point, but I'm not worried about it. The Moonlander has proven portable enough that I just take it home with me on the weekends and to off-site locations if I plan to spend anytime working on my laptop.
I have been very happy with Colemak-DH and made only one set of changes that are fairly small in practice (replacing Z with ' and ; with -). The motivator for those changes was to move the ' off of the right pinky, because I really dislike how it interacts with the other punctuation (particularly the comma and both slashes) when it's on the right pinky. As an added bonus, having the ' on the bottom row of the left pinky has transformed all of the common contractions and the possessive 's into really comfortable rolls or hand alternations.
If I could go back in time and remake the decision to learn an alt-layout, I would do so without hesitation. I would probably stick with Colemak-DH (with my minor alteration), but I know longer really care about maintaining the ctrl-Z, X, C, and V shortcuts nearly as much, so I would be tempted to try something more exotic like Semimak or Engram. But, I can't see any super compelling reason to choose against Colemak-DH, unless you hate alt-fingering NK / KN.