Windows Shells

I know of 3. Aston, AltDesk, and Litestep. Could anybody who has used them tell me what they are? I think I understand the concept of a shell, but what are the benefits of them?

Is Aston worth $29.99? (I think that's what it is)

What's the difference between Aston and AltDesk, both being made by the same group?

Is Aston better enough than Litestep to justify the $30?

Is AltDesk free?

Is the learning curve for Aston steep enough that after I buy it I won't want it?

If I use the Aston trial, is it like a Linux LiveCD where I can stop using it at any point and use regular Windows again?

Am I right saying that AltDesk is a shell?

Sorry for all the questions lol, but Aston has had me curious ever since I saw the "Post your desktops thread" and I was wondering what the people using it thought about it. I have to say, it looks much cooler than regular Windows.


Edit: After reading more about AltDesk, am I right calling it a shell? I guess I don't know what I would call it.