Since it is just a form and be used as a contact form I think it will work just fine with Classipress, imo. I haven't tested it though and so others here who have used the plugin can simply chime in.
Please help our moderating team work more efficiently by not sending us support questions via PM. You can read more about how AppThemes support works here. However, you can send a PM to follow up and remind me if I missed your support request/thread.
