What I mean by restrictive, is now I require Alby if I want to use my Nostr profile. So in the future if Alby restricts my use, or becomes a different company with different values (I don't expect this, but anything is possible) then my profile is stuck with Alby. Also, I'm sure I'm doing something wrong but I can't install Alby onto my phone so I can only use the desktop portion. I tried an extension with my brave browser and looked into the app store and there is no app.
The Alby Mobile Extension is currently only available for Firefox mobile on Android. We are waiting for Apple to fix an issue until we can publish it on iOS, too.
The Alby Extension is independent of Alby in the way that it is a fully client-side app. You can run it even when Alby should not be there.
But as @rabble said you can use the same Nostr private key in many other apps at the same time.