I've got both militia sets now from reptilian Overlords. While I have only printed a few parts, the prints look fantastic. I'm using a Anycubic Photon and its not really that difficult to use. The slicing software has a little learning curve, but once you have it down its pretty simple to use. Here is a blog post where I discuss my entry into 3d printing. with these two sets from RO and that new set from Grimforge, I'll be able to print militia, state troops, and great swords, plus warband models for Mordheim.
Selling 3d files is a way a small "shop" can get into business. Resin casting isn't easy. Plastic molding costs a fortune. Metal molding takes equipment and space. These designers might not have the ability to even make a go of being a manufacturer, so this is their way of sharing their work.