Running App as Watchface?

Since Garmin limit a lot with WatchFace to keep battery usage as low as possible. I'm wondering if we can use the app and run it (better if automatically start) 24/7 as a watchface with trade off some of battery?

Pros:

  • Can update as frequently as we want, sweep and or always on second is possible
  • Can accept key input and response as other watch: ABC changing, data fields changing, start/stop timer...
  • Tone/Vibration as we want it
  • Data update without limitation

Cons:

  • Battery drain
  • Garmin could not allow it
  • Need manually start
  • Can it run 24/7

Would love to hear from you all for suggestions and thoughts.