If you have to run potentially insecure executables, would using a separate laptop have any security benefit compared to a virtual machine, or would it be worse in the sense that the machine's firmware could be forever overwritten by malicious software, or the machine could infect other PCs in the local network? What risks do both solutions carry from a realistic point of view?
If you think that the executable is potentially unsafe, It is always better to access it in a network isolated PC. Considering threats like the recent zero-day vulnerability in VirtualBox (read more). We can never be sure of what's out there already. You can run it inside a VM inside the isolated PC with proper firewall rules configured as a safety precaution and always use up-to-date software.