But, hey, it's FREE. I've been using Mathcad 8.0 for MANY years and I don't need most of the high-end capabilities of Prime 2.0, so Express is a godsend. I can't justify ~$1400 or whatever for Prime 2.0, but I can sure justify free, even with the watermark.
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill