They’re fantastic little machines. I was looking for something small, but with the specs of a real computer. Everything I found was either underpowered, had terrible I/O (especially no RJ45 Ethernet), had terrible system resources, or was too big.
I uploaded HCL entries for every GPD Win Max model, and for the GPD Pocket 3.
I haven’t had any experience yet with other models, but I really want to.
My honest opinion is to go for the AMD GPD Win Max 2021.
A laptop with 16GB of RAM, a Ryzen 7 4800U, RJ45 Ethernet, 2 x USB-C with Thunderbolt 4, 2 x USB-A 3.2, full-size HDMI 2.0, AX210 Wifi 6, an M.2 slot for internal storage, a built-in Xbox 360 gamepad, PS/2 keyboard and trackpad, and multitouch touchscreen, crammed into a package just smaller than an A5 piece of paper?
Yes please! 
It’s got two fans instead of one, and using the gamepad for the mouse is a lot nicer than using a trackpad.
They also haven’t appeared to lock down the AMD BIOS at all, and you can customise everything, including things you probably shouldn’t unless you really know what you’re doing….
The only caveat is that Xorg seems to crash if you resume it from S3 sleep. If you can live without sleeping your laptop (until a fix is worked out), then it’s an absolute beast.
As for every other aspect of Qubes OS, absolutely flawless.
Battery life depends on what you’re using it for, but I usually get at least 5 hours off a full charge. Mind you, I’ve usually got 10+ VMs open….
Happy to answer any questions you might have.