@LemonadeCG
Looking at "pros and cons" of sketchfab I can say: they are the same parasites as Upwork, Turbosquirt and others. It's my personal opinion.
US style: "everybody should pay for everything and users problems are not our problems". Just wrapped in fizzy-dizzy-wow user interface and with potentially "hackable" 3D-viewer.
I have account on Sketchfab, but I don't use due to same reasons you described in "-", "+/-" and even due to some of "+" ("social aspect"... it's impossible to do JOB and "working on publicity" in the same time. At least for me ).
But again: it's my personal opinion.