A fantastic tool, I use it all the time now. It takes maybe 3% of the time that it'd take to do the same job in GIMP.
Use tips for newbies :
If you're getting an error from a particular Method, there's a "Select Methods" button that lets you trim that one out of the roster. If you find yourself reliably choosing results from a small handful of the Methods, you can cut the processing time roughly in half by only using those Methods.
If the whole thing errors out repeatedly, even after F5'ing the browser, just give it a few hours. I've yet to have it fail for me for two consecutive days in a row.