Success can be different at different stages of the company. So, what was the business goal with Google Hangouts? Or can I make my assumptions?
Business Goal: Tying users into the ecosystem of GSuite
Product Goal: Google Hangouts has reached a maturity stage, so it would be important to engage and retain users so that they continue using the service. This would allow users to consume more of the GSuite ecosystem (which is the business goal).
Google Hangouts helps users to communicate with each other. The communication can be with text, VOIP, video or by sharing files. The convenience is that it is well integrated into the Google platform, making it accessible across Gmail, Calendar.
There are different types of GSuite users:
Personal Users: Individual user accounts that use Gmail and other GSuite features for personal use to communicate with friends and family
Business Users: Business accounts using GSuite for internal communication.
Professional Use: Individual users using Gsuite in a professional setting like doing interviews etc
A user can start a conversation either from within Gmail desktop site, dedicated hangouts site or through the Hangout app. A user can create an invite to share with other users who they would like to join, so the other user doesn't necessarily have to have a Gmail account.
For Hangouts to be successful, it needs to ensure that there is a steady growth in usage, engagement on Hangouts.
For each of the above user group, the metrics that would inform/drive the business goal stated above are (all measured by user segment):
1. Number of users using Google Hangouts with more than one other GSuite product - As measured by segment
2. Virality - The number of invites sent to join Google Hangouts - this would help measure the proactive intent of using hangouts. Shows that this is the preferred tool for communication.
3. Average Length of chat sessions per user segment
4. Quality of Service - Number of interrupted calls, user feedback/satisfaction on call quality
5. Churn Rate - As there are so many other communication options out there, the switching costs are low. So, it is important to keep this in check, so that users are engaged on GSuite (which is the goal).
6. Engagement - Number of engaged users / number of GSuite users. Engagement is defined as actions taken (call / chat / share)
If the goal is user retention, the 2 important metrics to measure success of Hangouts is Engagement and Churn.