If you don't use the browser extension you would probably only want to use this feature if you control that Roundcube instance yourself because yes if you upload it to the server and your key gets lost all past and future communication with that key is only as secure as your keys password.
I have build apps with firebase in the past and the feature I missed the most was performing scheduled tasks on the database.
Now we are getting this BIG app platform update and this feature is still not in there. AWS Lambda with Scheduled Events for a long time to come :sad-panda:
Yes it is/was. The problem is/was that your app stops getting auto updates if you add permissions later. A lot of users never go into the update section and grant new permissions and so your app stays on the version with the old permission set for ever.
That law is a relict of the time before WW1 when Germany had an emperor. It just got adapted to the democratic system, so that it covers every head of a state. Everybody just forgot about it and it never got used since decades.