Man I just heard something about this the other day from a guy at the hardware store. He said the expensive stuff is mostly just marketing hype for people who think they need it. The cheap stuff sets up fine and sands just as smooth if you mix it right. I've been using the $8 buckets for years and my walls look straight as an arrow. Only time I could see needing the fancy stuff is if you're trying to do some super thin skim coat or something. But for 99% of jobs the basic joint compound does the job just as good.