It is a closed source proprietary software that requires to give up all your secrets to an unknown third party, and also pay per user for some of the features (and thus an unlimited amount if users are not employees).
Their ToS is also as abusive as it can possibly be, trying to take away your right to sue them in favor of arbitration (!), allowing them to terminate your service at any time, send your data to anyone unencrypted, disclaiming all liabilities and warranties, disallowing any content that is "objectionable", etc.
Their ToS is also as abusive as it can possibly be, trying to take away your right to sue them in favor of arbitration (!), allowing them to terminate your service at any time, send your data to anyone unencrypted, disclaiming all liabilities and warranties, disallowing any content that is "objectionable", etc.