My view is that if you're using push notifications you have to give control to your users. The best way of doing that is to make their 'alerts' as customisable as possible.
If it was me, I'd have a 'My Alerts' menu (or option in my settings) and from there I'd give users the following configuration choices:
- Who or what they want alerts about (eg. authors they follow, subjects they follow, articles they've previously read, trending now, etc)
- How they want their alerts (eg. email, SMS, etc)
- What triggers the alert (eg. changes to existing articles, new article added, article deleted, etc)
- When to receive their alerts (eg. immediately, daily summary, weekly summary, etc). You could also provide the option of picking a time for daily summary, or a day/time for weekly summary.
The above is only an example, the types of choices you provide will depend on your situation.
One issue you will need to determine is how you roll this out. Do you just automatically subscribe everyone with a default configuration, or do you just announce it as an enhancement for your reading app and just let users know it's there for them to try out?
Behaviourial Insights research tells us that one of the top 10 traits that people have is what's called a Status quo bias, also known as the 'do nothing bias'. Basically this is referring to the propensity people have for doing nothing, for just maintaining the status quo and take the path of least resistance, rather than making a choice and taking action.
Based on this you could just auto-subscribe everyone, knowing that the majority will do nothing and continue to get the alerts. I know of a number of organisations who have done this successfully. However, if you were going to go down that path, then I'd opt for a weekly summary at a set day/time and make sure your users know they can change the settings. A weekly summary will be a lot less intrusive than the potential for multiple alerts daily.
But, as I said, the most important aspect from a user experience perspective is to empower users so they can configure their settings or to opt out.