I haven't used TEDDS, but I got one of them demo packets 10 years ago or so. I was comparing it to MathCAD. I was so much more familiar with MathCAD that I preferred it.... though I could see how folks would like TEDDS.
One complaint that I had was how expensive they were. Really, I just wanted a way to make my hand calculations look neater / better. I didn't need anything really advanced. Just basic formatting (like a word processor) and basic math (multiplication, divising, subtraction, addition).
Both programs seemed very expensive for that purpose. I understand that the programs have a lot of power that I would not be using, but I always wished that someone would bring a simpler and cheaper product to market to compete with them.