Another happy UHK owner here.
I got the UHK since I was suffering from an increasingly troublesome shoulder impingement syndrome after working on laptop for years. The UHK was the best split keyboard alternative I could find which didn't require too much change from the laptop keyboard. Getting the keyboard and raising the laptop screen with a nice stand fixed my posture and the shoulder problems have been reduced a lot (together with physical training).
Now I'm feeling discomfort in my back/neck if I have to work on my laptop for a few hours, and I don't see myself going back to a non-split keyboard. Adding a vertical mouse to the mix has also been an ergonomical improvement for me.
Like the parent comment, I don't miss the arrow keys since navigation is quicker with the mod layer. I also use the Fn layer for controlling spotify many times per day. The agent software shipped with the keyboard is also great for customization, you can see how it works online here: https://ultimatehackingkeyboard.github.io/agent/
Disclaimer: I'm just a happy customer. The UHK is also the first enthusiast keyboard I've tried, so I don't know how it compare to others. I'd like to try the other types of layouts (like the columnar layout of the Moonlander), but it's hard to "risk" paying the price + shipment cost for those in case I don't like it, and living in the EU I need the ISO layout.