> I would only use it in a sauce if I needed to accommodate a vegan guest.

As an alternative, I've found methylcellulose to be pretty good for thickening my vegan homemade sauces (mainly tried it because I use it for other stuff, like fakemeat homemade protein sources). That's for homemade mayo or the like; for sauces in stews and similar, flour does the job - though US cooks seem obsessed by cornstarch instead for that use case.