Why should I buy this without any documentation?

What makes you think this chaotic forum is adequate? You are absolutely mad -- you are at the top of google for everything realted to grids, ajax etc but only the foolhardy would attempt to tackle your product as the documentation (or lack of it) stands. What a wasted business opportunity.

I can't say that documentation is great but did you actually look here -

http://www.activewidgets.com/aw.ui.grid/ ?

Did you look in /examples folder in the download package ?

Would be a lot more helpful if you say what kind of documentation is missing - introductory articles, server-side specific code, what exactly are you looking for?