I'm using these inside an air tight box for storing my 3D printing filaments. So far its doing the job, too soon to tell long term.
I put 1 of these bags into my (large) box and it brought the humidity inside the box from the abient room humidity of around 50% down to 23% in just an hour or so.
So far so good! And they feel sturdy and well-made unlike others I've tried. Quite expensive, but it seems worth it if you need something like this.