Unless something changed or I'm mistaken, I believe that System76 are just rebranded Clevos (http://www.clevo.com.tw/). In the U.S., Sager has the contract for distribution (https://www.sagernotebook.com) and I believe they're the ones who resell to people like System76, XoticPC, etc.
As far as these computers, I own and use a Sager NP7338 (Clevo W230SS) that I purchased through XoticPC. Works perfectly great with Linux and Sager has been pretty easy for me to contact directly and get replacement parts (a keyboard so far.) Mechanical quality is only fair. Had some problems with the hinges, which I ended up drilling out and putting in some bolts, but other than that I've been extremely happy. I've three SSDs in a 13" computer with replaceable batteries, so I've gotten plenty of good use.
For a supposedly Linux-oriented vendor, System76 does less than you would expect to pick open-source friendly components: they offer NVidia discrete GPU options but not AMD, and use Intel WiFi instead of Qualcomm-Atheros. I wonder how much effort they put into ensuring that the rest of the system works well out of the box with Linux, especially where power management is concerned.
Is Intel Wifi bad? All my notebooks use some sort of Centrino chipset and I've never had trouble with it, although I recall friends having trouble with their Atheros chipsets. (But that was nearly a decade ago...)
Atheros 802.11n chipsets are the only WiFi devices that don't require any proprietary drivers or firmware (since 2008). Consequently, they're the first and sometimes only devices to benefit from new features added to the Linux WiFi stack. Qualcomm-Atheros 802.11ac chipsets require closed-source firmware like all 802.11ac chipsets, but the QCA firmware is actively maintained by people who have source access under NDA, and they generally try to make sure that the firmware exposes the functionality the open-source Linux driver wants. Atheros and Qualcomm-Atheros chipsets are also the most common WiFi chipsets with open-source drivers to find in routers and access points, so those drivers get QA and widespread testing in both client and AP roles.
Intel WiFi is in a lower tier of support, where you can't count on having access to the full capabilities of the hardware (eg. apparently power management hasn't been working for quite some time, and AP mode is only available on 2.4GHz). But at least Intel WiFi drivers are open-source, so it's clearly a better choice than Broadcom.
Perfect software-hardware interaction, but the build quality is horrible. My laptop has a hard shut down once a week presumably because something power-related is loose. The screen also gets scratched against the base when closed.
