We use RVSitebuilder as well but it has various problems. The main issue is that they don't test it at all. All testing is done by customers. Hence there are always a lot of bugs. Also the product does not look very professional. Some of its features are difficult for our customers to use. Translating it to a another language is a pain. Constantly you will find things that cannot be translated.
I wish somebody would make a decent sitebuilder that is fully integrated to Cpanel.