The 4012/W500 is the high perfermance reducer. The 4011/W100 works well, but the newer one is superior, has even better flow, less tip dry, harder cure etc. If you want to use erasing techniques you might want to use the W100/4011 as there is a smaller window to work in with the W500 with the quick drying and hard cure - however surface plays a big part in that too. On a decent surface I don't have an issue, and much prefer the benefits of the high performance reducer. The 4012 /W500 is also a great cleaner, back flush a couple of drops, clean out then spray a couple of drops through, and your nozzle will stay squeaky clean. Not the most cost effective perhaps, but it really only takes a little and worth it to me to have a great performing gun.