When comparing Messenger vs Yammer, the Slant community recommends Yammer for most people. In the question“What is the best team chat software?” Yammer is ranked 37th while Messenger is ranked 74th. The most important reason people chose Yammer is:
To make it easier to learn for new users and increase adoption.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Uses Facebook friends to create a contacts list
Allows communicating with anyone who's a friend on Facebook.
Pro Read receipts
Can see who has seen each message in group messages.
Pro Easy to share posts from Facebook
Integration with Facebook makes it easy to share any interesting posts from the Facebook timeline.
Pro Great UI
User interface of the application is clean, intuitive and easy to overview.
Pro User interface is modelled after Facebook
To make it easier to learn for new users and increase adoption.
Pro Hashtag support
Hashtags help organize projects and parts of projects easily. Great for getting an overview of a specific subject and seeing if something's missed.
Pro A complete social network for business
Yammer works like a typical social network with status updates, comments, file sharing, groups, etc.
Cons
Con Lack of privacy
Messenger is owned by Facebook. Based on their privacy policy, this means that any information you provide (including messages sent) are used by Facebook to profile you and sell access to your data to advertisers.
Con Lack of end-to-end encryption
Secret (end-to-end encrypted) chats are only supported in one-to-one messages, and are not enabled by default, and the encryption has not been verified independently.
Con Lacks customization options
