You can use GameSparks as your main Push Notification service. Push Notifications are a great way to engage your players and improve retention.

However, please be aware of a few things:

• Sending a Push Notification in GameSparks will flag a user as a returning user for the current month, and you will be charged accordingly, even if they haven't logged into the game for that month.  They will be counted on the Analytics > Overview > New / Returning Players chart and also count towards the big numbers at the top of the page - DAUs, MAUs, and so on:

• GameSparks is only really interested in sending the message, but has no visibility on whether the message was successfully delivered to players' devices. However, you could write some custom client logic that tracks the success rate of opening a message. This should be fairly easy to implement via the message listener and will let you measure engagement.

For information on how to configure Push Notifications, please refer to these articles: 

• Configuring IOS Push Notifications
• Configuring Firebase Cloud Messaging Service Notifications