The ability to use it as part of our CRM system has been great - we've had so much success using it that I'm not sure what else you could ask for! As mentioned above, however, the fact that they don't integrate into Salesforce (at least at this point) has meant having to export data from each other manually, which can be quite tedious.
They do provide some integration tools if you need them, but there are better options out there. However, since their solution integrates with most third party platforms such as Marketo, HubSpot, etc., we were able to get around this limitation by exporting directly from those services instead.