I just did this (with win2usb) and everything is working fine except the CPU is running too hot so it shuts down my laptop after about 5 minutes, which is very annoying bc everything else works fine,
it does take about 2 or 3 minutes to load Windows, I only want to use it for software and hardware that won't work in Windows 10 even in Compatibitily mode so it's not something I would use all the time (only when needed) so the long boot time doesn't bother me.
You do need to set it to load off the USB drive (pushing escape key when booting and then scrolling down to set it to boot the right software, I did have to change the bios to be able to load this way (turn off boot security and allowing it to load off csm (I don't even know what csm is but I had to allow it before it would boot off the USB HDD) anyway if I could solve the overhot CPU problem everything loads, I installed all the device drivers, etc).
I have to say if Windows would just let me put my Laptop back to Windows 7 I'd do that (Windows 7 worked with all my HDD and Software while Windows 8 and now 10 doesn't, even in compatibility mode).