A few days ago I received my DIY Framework laptop as well. I also have a MBP 15" circa 2018. The keyboard issues on the MBP was my primary gripe with Apple, also reading the 55 steps needed to replace the battery according to ifixit guide.
I first discovered frame.work on hacker news, watched a ton of youtube videos and got all jazed up and bought one, then waited for it to ship (about a month since they do it in batches). I actually never had been this excited about a product as this, and would read up on their site daily, to prepare.
Anyway, it arrived, and I assembled my first laptop! The hardest part was hooking up the wifi, but with a little thinking it worked. Took about 10 mintues, with kids running around the background.
Having a month to ponder all of the flavors of linux, I was initially jazed about NixOS as well. I'm not a daily linux user and reading through the documentation was discouraging. There doesn't seem to be a simple way to install it that I have discovered. Eventually I discovered Fedora Silverblue which has the same concept of an immutable OS. I still want to try NixOS, but I will need help with that. Another nice thing about these devices, you are free to install whatever you want on them, unlike Apple which locks it down. The Fedora Silverblue installation was about 4 minutes, minimal decisions to make. So that is what I ended up with.
At first I tried version 34. This did not work immediately with the WiFi, and that had me concerned (what if I didn't hook it up right?). LOL.
So, I tried the RAWHIDE release (which will be version 35). Mostly I did this to see if the wifi worked and it did! After playing around with it, I started getting used to it. It works with wifi, the fingerprint reader (great), bluetooth, trackpad (see comments below).
Build Quality.
The Framework build quality is excellent. It's much lighter than the MBP, and I think the reason for feeling a bit more 'flexible' ie bendable is the lack of glue. I think the glue also helps the accoustics. The speakers are definately a disapointment compared to the MBP. That said, I would trade ability to swap out battery for feeling more solid. Maybe this can be improved, but to me it's not a huge issue.
Trackpad.
I am not entirely used to linux, so at first I didn't know what was a hardware or what was a software issue. The two finger scrolling works, as does three finger navigation, but scrolling on the browser sucks. Two issues, acceleration is a little wonky (no rubber band feel), and scrollbars are always visible. The claim is that wayland does not have some universal scrolling system but relies on each application to implement it. Firefox, chrome, Ungoogled Chromium all seem to act the same. Some of this might be Fedora 35 which is still being developed. That being said, I've tried recent windows machines this experience is better than that. I think the MBP does have a smoother experience here, but this is usuable for sure.
I am now starting to get used to the linux experience (gnome). I like the screen, wish it was a bit bigger, but certainly usuable.
I have yet to get a second or third monitor working on here.