Anyone have any opinions on warm coats/jackets that can be smushed down very small?

Mom got me a nice winter coat from LL Bean, which doesn’t fit, so I am returning it for a different one. Any reason I shouldn’t have them refund the money to her card and buy a coat off eBay? (I told her I was probably going to do this.) Is Primaloft actually significantly better than Thinsulate, etc? Is it possible to pirate Aerogel yet