What I will say is that the machine I used to use in the van lost its video output (the perils of onboard graphics), and I've found it impossible to source a reasonable replacement mobo. As a result, I've switched back to using a laptop (lenovo Y700) in the van.
What I notice as a potential improvement is that it effectively lets me store an extra X hours of power for computing, because I'm adding the laptop battery to the overall storage. Compared to my "house batteries", the laptop batteries are of course very small. But getting (say) 3 hours of work time stored up in the laptop does seem like a plus, especially on cloudier days.
It's also increasingly common to see single-board SFF desktops that are essentially laptop parts with different I/O. I suspect that those are less heavily tuned, though.
at home now i have a 16 core ryzen, which is extremely quiet and very, very much faster than those systems. but i don't think it would be possible to host this on a 12VDC PSU, and even if it was, the mobo form factor is inappropriate for the space i built in the van :(
to be fair, the lenovo Y700 was/is essentially as fast as the 12VDC systems, which is quite impressive.