Very easy implementation of our data management system for mobile users (iOS/Android) from within Salesforce Data Sync Service! They even have an app that makes it very simple for sales reps who are not familiar at all how this works but just need something quick like "just sync my contacts". Great support team too - I've never had any issues getting help when needed! Nothing so far actually since we launched last year. Would be great if they could integrate their billing platform into SFDC somehow though? We're solving problems related to CRM integration between different business units which use multiple platforms (Sales Cloud + AppExchange).