Why switch?
I played with the idea of switching for quite a while. Having switched my daily driver from Windows maybe 6-9 Months ago I made many mistakes in the meantime.
Good and bad
This may have led to a diminshed experience with ubuntu but all in all, I was very pleased to see that Linux works as a daily driver. Still, I was unhappy with the kind of dumbed down gnome experience.
Problems
There were errors neither I nor people I asked could fix and the snap situation on ubuntu (just the fact that they’re proprietary, nothing else).
Installation
Installing debian (and kde) was easier and harder than I expected. The download mirror I used must not have been great although its very close to my location because it took ages although my internet connections is good.
Apps
Since I switched to Linux, I toned down my app diet a lot. Installing all my apps from ubuntu was as easy as writing a short list and going through discover. Later I added flatpak which gave me a couple apps not available through discover (such as fluffychat). The last two I copied directly as appimages.
Games
I was scared that the „old kernel“ of stable debian would be a problem. As it turns out, everthing works great so far, a lot better than on ubuntu which might or might not be my fault.
Instability
Kde does have some quirks that irritate me a bit like installing timeshift (because I tried network backups which dont work with it and the native backup solution does not seem to accept my sambashare) led to a window I could only close by rebooting.
Boot time
What does feel a bit odd is the boot process. After my bios splash, it shows „welcome to grub“ and then switches to the debian start menu for 3 seconds or so, then shows some terminal stuff and then starts kde splash and then login. This feels a lot longer than ubuntu did. Its probably easy to change in some config but its also something that should be obvious.
Summary
So far I‘m incredibly happy although I ran into initramfs already probably because of timeshift which I threw out again. I might do a manual backup if nothing else works. My games dont freeze or stutter which is nice. All apps I had on ubuntu now work on debian and no snaps at all.
TL;DR: If you feel adventurous, debian and kde are a pretty awesome mix and rid you of the proprietary ubuntu snap store. It also doesnt tell you that you can get security upgrades if you subscribe to ubuntu pro. Works the same if not better.
Depends a lot on what kind of user. I specified "non-technical" with a reason. I have, in the past, recommended Ubuntu to a small number of friends and family members. These are people who aren't particularly comfortable using computers in the best of times. They very much don't need the newest, best and most shiny versions of everything. They need to do billing, taxes, correspondance, email and various other tasks related to their small business, they need that to work reliably, and if at all possible, to work exactly the same way as it did the last five years. And if there is any pop-up they don't immediately understand (for example because it's in English instead of their native language, yes that still happens in Ubuntu quite a bit), they will call me on the phone.
I don't know if you've ever had to support non-technical end-users, but for some of them, even something as seemingly trivial as a menubar that has moved from the top to the side can be issue that needs explaining and training. For that kind of user, I really do want to postpone all updates beyond pure bug and security fixes for as long as reasonably possible. Five years sounds reasonable. Six months does not.
Ubuntu is not Arch Linux. The 6 month release doesn't give you the "the newest, best and most shiny versions of everything" in the first place.
If they don't like change so much as to not being able to handle some minor UI updates, then their better off using a Chromebook lol.
You'd just be making it harder for them to move from the outdated software in the long run, because literally everything changes between moving LTS from the 5y EOL period instead of gradually over each major normal 6 month releases.