Obtain results at screen transition destination using RxJava on Android

I think there are several implementation approaches, but I often use the following two:

• Set Observable to Hot in FirstActivity (I often use replay or BehaviorSubject)
• Give Observable to the Application Class and issue a key at that time
• SecondActivity uses the key to remove it from the Application class after the screen transition

• Create a Service that is responsible for asynchronous processing itself
• Request FirstActivity to Start Communication with Service
• Bind on the SecondActivity side and wrap it so that it can be treated as Observable

1 is easy to implement, but it is not suitable for critical processing because handling is troublesome if the activity transition is not successful.I think it is difficult to implement 2 while the service can bear the responsibility.
When I implement it, I try to use the approach of 1 for retries and 2 for those that require precise health management.