I was excited to read this app could handle scheduling via on our website, until I found out it uses Sites, a deprecated feature of Salesforce that is no longer supported or enabled on our org... So this takes away a good part of the usefulness and makes about 50% of documentation obsolete. If you can't use the calendar or any of the website features, not sure how much use we'd get out of it.
Is any update planned to restore this functionality for non-profits, or updates to the documentation to reflect more current functionality?

@TM SFDC Admin, As I understand it, the issue with Force.com sites is they have effectively been replaced by Salesforce Communities. Officially the product isn't deprecated, but in order for users to login (authenticated users), they must have a Customer Portal license. This license is no longer available to new Salesforce customers. If you were a Salesforce customer before this change was made, then you may be grandfathered in.
All of the above is mostly irrelevant as it relates to V4S, because V4S users login using the Guest User Profile, which doesn't require the Customer Portal license. V4S is still a solid bet for the use cases that it serves well. If you have a use case beyond that which is presently supported by V4S, Communities and some of the other 3rd party apps out there are worth a look.