I've updated the main post to call them "Free Previews via API" instead of "Free Credits" since that's what remove.bg refers to them as - I had these in my head as "free credits" rather than a "free" paid credit if that makes sense - the plugin will resize your images back to their original size, so you'll see a slight loss of quality using these previews.
I'm not affiliated in any way with remove.bg, I wrote this for my own personal use as a PDN user and figured others might find it useful!