Since only a fraction of vehicles in France bother with crit'air, and there is nobody checking this anywhere, I wouldn't worry too much about it.
I was recently in south and east of France on vacation, then work, and I paid specific attention to this as I didn't have one on my company car. Some of my coworkers are in Strasbourg and Paris every few months and none of them has even heard of this sticker. No fines ever came either over past several years they've been going there regularly.
The whole scheme seems more like a non issue, regulation that never actually got enforced.
Seems to be nearly the same with the german equivalent. Many more cars have it though. Yet enforcement, at least on foreign vehicles, seems non existent.
Unless you have the time to order them, not much of an expense really, I wouldn't bother.