Emmc is forgone with Linux due to some driver issue, but I wasn't intending to use it anyway.
Probably either the way it's talked to or the way it implements power saving modes. I got the impression in these cheap devices that the engineers like to go wild with GPIOs (yes, your "fully-grown" Intel/AMD SoC has GPIOs just like a Pi, they're just usually either used for board-internal things by firmware like letting you switch things on and off in the bios or just not wired out) to control them, something often quite custom the linux drivers of course know nothing about and never will as no developer gonna sit down and implement it for some cheap celeron netbook. As good as hardware support has gotten for Linux in recent years, if you buy mobile devices like this you can quickly end up in no man's land regarding specific features if you get unlucky.
I decided to keep the Fujitsu Q616 as the thing has a robustness and kind of old-school-y feel about it you don't find in other devices today. It's also well built and one of the few mobile x86 devices I know of that actually comes with appropriate passive cooling. Under continuous load, the CPU hits at most 50-55C and immediately also drops ~10C as soon as that load is removed. Barely gets warm on the case. This is often an overseen thing in these x86 mobile devices, especially in the push to make them as thin, light and elegant as their ARM brethren. (which this one doesn't even try to be) Some of them advertise CPUs that are fast in theory but in practice never will be able to reach their top speeds because of inadequate cooling, being slower than devices with slower CPUs. They might get up to higher bursts for short times but depending on how you use them that might not make much of a difference. The heat they sit at is also often hell on the batteries (Li-Ion doesn't like heat at all, especially while charging or sitting at high voltage) and my theory why some devices are just notorious for failing batteries, as on the inside they're all using the same cells anyways.
The 1080p screen at 11.6" isn't quite HiDPI and my biggest critique (16:9 is kinda the pits in general and I fell absolutely in love with that HP screen) but it's serviceable and still quite high-density and generally a good screen with good color coverage, contrast, etc.. so really nothing too shabby. Interestingly, the SD card reader is not an USB device but connected via PCIe and quite snappy with one of the good cards I have as a result. (one of the small details that shows that this was originally a ~$1.5k device) I also got a 4G modem I already got working and plan to get a SIM card for so I can do some SMS scripting and the gigabit ethernet adapter is actually in the device, the ethernet port in the cradle is just wiring it out.
The bios hasn't locked undervolting so I've been doing that amongst other tweaking. I've seem to have won the silicon lottery since I could push it quite far before becoming unstable. The result is that I managed to push the device down to 2.5W idle when the screen is off, which is in the Rasperry Pi 4 range if google is to be trusted. (the probably better PCB layout and used components play a role, as does my slim linux setup with very few background tasks. I used to have a Pi 2, I was NOT impressed with the build quality for the price) Playing back video with hardware acceleration and/or normal browsing with script blocking now puts it somewhere at 5-6W with the screen at 60% brightness which might be a bit more than a Pi, DOSBox emulation (playing System Shock) puts it at 9W average. To make the comparsion fair in regards to the Pi, you'd need to substract the 2-4W that go to the screen (the Pi's measurements you find online are all without screen) and are included in all my figures here as the intel chip does fancy things with the display refresh like framebuffer compression, self-refresh and partial refresh which makes it kinda hard to get a constant figure from the screen itself. I got curious and actually turned the screen off while running around blindly in System Shock as increased difficulty mode, power consumption dropped to 5W.
Peak is still at around 11-14W but that happens rarely outside of benchmarks. When it comes down to it, the unit sits in a power consumption bracket very close or the same to ARM boards like the Pi. While doing that, it also comes with a case with appropriate cooling solution, a battery, a keyboard, a cradle (with USB 3.0 ports and both a displayport and a VGA port, the unit itself has a mini-HDMI port), an inbuilt high-quality screen, 8 GB of RAM and 256 GB of fast, replaceable SSD, WLAN/Bluetooth/4G not to mention extras like an inbuilt wacom tablet with 2048 pressure levels, a touch screen, a card reader, a GPU that's actually doing the full OpenGL spec. and is software-supported for all decoding algorithms it offers, excellent hardware support that won't be dropped anytime soon by Linux and compatibility to common software. How people still like these expensive ARM boards while shitting on used computers like this is beyond me. I don't know current prices but I'm pretty sure if you buy a Pi 4 with hardware peripherals you're already way past 150 bucks. It's just not good value. Also, buying used devices like this is better for the environment than buying new and even if they consume a bit more than newer devices, you overall end up saving the planet energy. (You'd often have to use the slightly less power consuming devices for decades to make them worth it in their energy cost re: production, transport etc.) Speed-wise, they're very different hardware platforms and difficult to compare but according to 7z benchmarks I could find for the Pi 4 they put the Core M at roughly double the speed with it's two cores and HT disabled vs. the four hardware cores of the Pi. (enabling HT here could actually help for once since it would improve throughput, I just couldn't be arsed) Since a lot of programs are still heavily single-threaded like aforementioned emulation, this would probably make the Core M a lot faster in practice.
I could find only little info about the Q616 besides that it was first released in Japan and apparently is more targeted at bulk-buying enterprise buyers, not end users. It's also marketed as "semi-rugged" device, fujitsu also makes a full-blown rugged version with water resistance and all the bells and whistles. Fujitsu has quite the history when it comes to tablet computers that goes all the way to the 90s, so my guess is they know their stuff. Really like the build quality on this one. Really also like the idea of convertibles since I hate notebook keyboards.
EDIT: Because this post is a fervent advert for using "outdated" computers, I do want to point out a downside - the lack of some new technologies. For example, the HD 515 GPU in my chip isn't really VP9/HEVC capable yet. (it can do HEVC *somewhat*, but not really the interesting profiles) The HP Celeron Netbook I have might be a piece of shit and much slower otherwise, but it can do such. In 1080p video (the only resolution that makes sense on the screen) it comes down to a difference of about 1W in decoding between a "supported" H264 video in hardware and a H265 10 bit video in software. This is still much more powersaving than my desktop's iGPU who just decides to ramp up by 10W to do either in hardware. It's still a thing to be considered and would have an effect on battery life time in my case, even if minor. The impact would also be much larger if I'd want to e.g. watch a 4k H265 10 bit video, the N4020 would fare better there.
