It slows the dry a bit and lets it smooth out, but doesn't thin it and make it runny like the thinners do. I use it in any oil base paint or varnish. (Pettit, Interlux, Rustoleum, Minwax, etc.) I find if it is a big job I have to add a splash from time to time.

I don't use the proprietary thinners. For cleaning brushes I use mineral spirits, then soap and water and dip them in denatured alcohol to speed drying (if desired).

Home Despot has it for a lot less than Worst.