Dear customer,
I've a team of Drupal developers from year 2007.
We've develop some project using the Service module of Drupal (for D7 and D8).
In particular, we have developed an APP (first with PhoneGap, and 2nd version with Unity 3d), using Drupal as platform to create similar features in the WEB, and also as repository of database, where we store info of profiles, products, events, calendar, chats, and also a system to provide suggestions (with notifications), banners with a full synchronization, since the 1st time is opened the app until the notifications of emailing with offers or remember actions, etc..
Kind regards