Just a quick thumbs up from me - as I've been operating my Ubuntu setup that way for many years (from at least 12.04 LTS if not longer).
However I don't use a flash drive - instead I use a portable hard drive, which these days mean USB3. While this is mostly about capacity, where I did use flash drives I found they didn't last as they're really not made for frequent data rewriting long term.
At some point you may have an epiphany when you realise that your USB drive now "is" your computer, and the computer is now the dumb piece of commodity hardware. As a bonus, the hard drive is much more portable.
The one big catch however - and you clearly already found this - is that you need to learn how to "get into" the boot sequence of any computer you go to use. In general, each different make+model is .. different.
A related catch is about the alternative booting schemes - MBR versus EFI. At this point, I'm still finding it more reliable to use MBR boot on my external drive, as the Ubuntu update process for EFI defaults to updating EFI on the host machine instead of the external drive. In 2019 this seems a dumb choice to be making but I haven't yet found a good enough work around.
FWIW - I prefer to find which method does not require making a permanent change on the machine - and yes, even on my main machine I tolerate doing the couple of steps to divert the boot on every power up. But another good method is to install REFInd - en.wikipedia.org/wiki/REFInd - there are quite a few options for boot managers around. After years mucking about with those, seeing the external drive as "the computer" led me to stop bothering.
p.s.in case it's not obvious, having a full hard drive - e.g. 1TB - means I do a "full install" onto it, not just the downloaded boot image.
Mind blown! Why didn’t I think of that!? I’m gonna look into getting an external hard drive. What a great idea!
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