@happy0 gives an excellent related answer here:

I'd strongly recommend you don't share your key between multiple devices to use your same scuttlebutt profile on them. You might run into this situation:

1. You have posted 10 things on your profile. Device 1 is offline.
2. You post something on device 2 (you now have 11th post.)
3. You post something on device 1 before it has synced your own feed from other computers.

4. You now have 2 versions of your 11th post. Other computers have 2 versions of your 11th post.

5. Any time you make some posts from device 1 or 2, some computers reject them as invalid as they have a different version of post 11 (and all the posts onwards.)

6. One of your feeds is now invisible to a lot of people after post 11 as they agree that the 'real' post 11 is the other one.

To be safe, I'd use 2 different keys and wait for the 'sameAs' functionality to be implemented that allows you to safely share an identity between devices.

If you must share the same key between devices, then it should be safe if you share the entire .ssb folder (the database, not just the secret file) over a network share between the devices. That way all the devices always have the same view of the database as they post as it's the same underlying folder.