It simply provides another download option via Google Play. But you can also download the APK for installation from Zapstore and GitHub.
Does the version on Zapstore not use GMS?
It’s not using any GMS API if I haven’t missed any code. Even for FCM push notifications, it’s using FOSS-FCM. https://codeberg.org/UnifiedPush/android-foss_embedded_fcm_distributor.