This is from years back, but my experience is that running Windows from an external drive isn't really easy. I hardly use the OS any longer, but I'd like to keep it around on an external drive if possible.
apparently some USB flash drives have a bit you can toggle with some vendor specific tool, but I've not tried that
for a non-removable device installing Windows is exactly the same as for a normal hard drive (no fuss with Windows To Go or other rubbish)
This is from years back, but my experience is that running Windows from an external drive isn't really easy. I hardly use the OS any longer, but I'd like to keep it around on an external drive if possible.