Best
Android with latest versions of Google Chrome, Samsung Browser, Xiaomi Browser, Huawei Browser.
Not so good
Windows desktop traffic.
Traffic to completely avoid
iOS, OS X
In-app Webview traffic — when the landing page is opened in an Android Webview browser inside an app — makes it impossible to subscribe the user to Push Notifications.
Iframe: If the landing page is opened inside an iframe, it's also impossible to obtain a subscription.
Traffic from Incognito of Private browsing tabs - for the same reason.
Very old versions of Android and Chrome that don’t support Push Notifications or have poor quality users.
Use Proxy traffic!
Some traffic sources allow you to target Proxy traffic.
This traffic comes from users who use Proxy services to visit sites that are blocked in their countries, or for privacy reasons.
Proxy traffic is typically inexpensive because many advertisers consider it low-quality and prohibit it on their offers.
But in the case of Push Subscriptions, this traffic can be used because after a user disconnects from a proxy, they will continue to receive ads via push notifications.