Yes, I know that works too! 😊
I had a very bad experience with deb-multimedia.org, the apt decided to upgrade things using that repo and broke a lot of things on my system, so I pass. It took me a lot of time to discover that Opera requires that environment and not just the so in the right place.
Now the news is out there, there is no more need to use deb-multimedia.org and any Linux system can make use of it. I don't use flash anymore, my config is set to block it, but for those that need it.
It's possible to run scripts or commands apt after an upgrade or update comand:
If people are so in need of flash, it's possible to create a script to update not only flash but libffmpeg also among with the trivial apt-get update && apt-get upgrade.