Right now we are using CCB - though I find both Rock RMS and CiviCRM extremely enticing.
(That said, I have / do work fairly extensively with open source, both for Liquid and for other projects I have / do work on)
I can provide you with three critical areas I’m currently hitting my head against the wall with regarding CCB that wouldn’t be a problem if the solution was open source:
User Interface Customization
CCB allows one to substitute one’s own logo and add some welcome text on the login page, but beyond this there is very little one can do about CCB’s appearance (e.g. colors, fonts, layout).
Unfortunately, the CCB API is missing at least one critical component - a full implementation of their Forms API.
This might not seem crucial, but it is because of the way CCB handles incoming data for events, etc. I’ve run up against this as we have been trying to create a WordPress plugin that syncs data between Gravity Forms and CCB.
For example, when one creates an event in CCB, the data used to provide a quick dashboard report on the event is collected from data accumulated in the Forms rather than associated with the actual event. Since one cannot write to the Forms API, there is no way to attach this data to the Forms, and thus no way to include it in the reports. This leaves us with the option of building a completely separate reporting apparatus (not ideal)…and there are also issues of registration duplicates since the Forms code in CCB seems to handle a lot of the deduplication logic.
CCB provides a groups list that is searchable/sortable but that isn’t customizable. We’ve been working on a groups plugin as well for WordPress, that pulls in data from CCB and displays in a style that matches our site.
Hope this is helpful!