Is it the ad-free tier? If so, both the native app and Apple TV app will provide 4K with Dolby Vision. As for sharing the subscription, you will have to share the login. Their native app also allow features like downloading for offline viewing and 3 simultaneous streams, same as Apple TV Channels.
The only real reasons for subscribing to Paramount+ outside Apple TV Channels is for:
- You prefer Paramount+ app's profile management
- Ad-supported Essentials plan
- Annual pricing option ($99.99/year)
- Paramount+ SHOWTIME bundle ($12.99/month or $129.99/year)