I've been using a System76 laptop for about a year and a half, close to two years, somewhere in that range. I initially thought I would ditch PopOS for something I was more familiar with, but in the end I wound up keeping PopOS.
Overall impression? A+++ would buy again.
I've been very happy with the machine and actually wound up liking PopOS enough to stick with it. No major complaints, everything "just works". The one thing though, is I splurged a little bit and got a machine with 64GB of RAM, plus both an nvme drive and two SSD's. So my impression of this machine may be colored by the fact that it may be the first machine I've ever owned where I truly felt like I had enough RAM and enough storage space, to not have to think about either (for the most part). I can now have like 8 browser windows with an aggregate 400 tabs open, have three, four, even five separate Eclipse instances running, Okular with a few PDF's open, an OpenOffice doc or two, and everything just hums along. No swapping, no drive thrashing, etc.
Wish I could tell you more about the "non PopOS" side of things, but I just didn't wind up going that route. The one thing I might suggest, is that if you buy a System76 machine, give PopOS a long hard look yourself, before deciding to ditch it. You might also decide to just keep it. YMMV, of course.
