You’re right to be wary of unlimited. It’s primarily a way for employers to avoid having to pay out accrued vacation time when staff leave. And create the competitive environment you mentioned over taking few days vs a lot. It seems great at first glance but I’d prefer a set number of days, no ambiguity that way.
I order mine from https://smol.com/uk. They come in a cardboard packet which fits through the letterbox. I was also fed up with the ridiculous and unnecessary amount of plastic in the supermarket equivalents.