For the most part I liked them. If you had an issue with the theme and it was a bug in the theme, they would help you to fix it. If you want help with minor design changes, they didn't help that much. They would only help if it had something to do with a problem in the theme. I can see the rational in that to an extent. They can't help everyone design a blog.
That said I have worked with Elegant Theme websites and they seem to go out of their way to help get the functionality out of their themes. I've seen where they have given rewritten PHP code to people get things the way they want.
My latest theme is with Themify.me http://themify.me/ They seem to answer most questions and the theme's control panel literally allows to you to style almost anything without going into the CSS stylesheet.
Basically I have been happy for the most part with all. If you feel comfortable with designing and the stylesheets, WPzoom is fine. If you are newer to it, you might want to see if there is a theme with one of the others.
Hope that helps