I just picked up a moonlander that i'm really living.
Ortholinears, of course, are all exactly the same, which lets me type with more confidence. I don't type any faster, but I do suffer fewer typos for words that require multiple row switches.
Ortho keyboards got me in the habit on using modifier keys on the opposite side of the keyboard from the shortcut key. On a regular keyboard, I'll type Command + c with my left thumb / left index finger with an unergonmic movement. On an ortho keyboard, I use my right thumb + left middle finger for the same motion.
For Vim, I started using Control + c to escape with ortho keyboards, which keeps me on the home row.
None of these are huge productivity gains. But a fun way to shock your brain and to stay sharp.
In my example, I type around 80 wpm on a regular keyboard, but I've never learned and used the proper key->finger assignment - I just type how I adapted over the years. So for me there was no trouble switching to proper technique on an ortholinear. I'm not yet nearly as fast, but it feels like it's 3-4 times easier to type (ie. less finger movement).
I'd already spent the time to learn Dvorak layout on row-staggered keyboards. Having had that training, picking up an ortho was straightforward. (Although my average wpm on typing tests after picking up the board would've been ~90).
I suspect if all your fingers 'know' is where the keys are (rather than following discipline of 'column per finger'), then adjusting to ortholinear would be harder.
Since I printed/wired myself a dactyl. Great little kb.
I was at full typing speed within a few days. Main problem was getting used to the custom locations of modifiers (e.g. thumb clusters).
That's what happened for me, at least.
This was also going from 60% to my first split/ortho.
Took me another couple of days to get used to chording and these days I use a 36 key split board.
So your mileage may vary, but it's definitely not going to take you months typically.
The only thing I had to relearn were the keys on the bottom alpha row on the left side, because on a regular keyboard I would tend to offset them by one column (i.e. type C with the index, X with the middle finger etc...) but with an ortho I didn't need to anymore. And the only reason I needed to offset them in the first place is because standard keyboards have such a bad layout for the left hand.
They say you can tilt the thumb clusters up, but then you lose the ability to tent the keyboard.
If you tent it, the thumb cluster is doing the work and has to be tilted down making it harder for smaller thumbs.
They should have provided another leg to do the tenting so you could adjust the thumb cluster as needed.
I don't regret my purchase but if I were you I'd wait for something a bit more consequential, maybe a Moonlander Mk2. Or a more drastically different keyboard, like a manuform or a kyria for instance.