That tool appears to be getting the firmware from brother servers. They have removed the old firmware as of more than a year ago (this issue is not new)

Is there anything useful usually in those fw updates?

Probably some dubiously useful features such as a nicer web UI (I never use it anyway), some utterly useless features like "scanning to Dropbox/GDrive", or most probably now some "AI assistant" that tells you how to switch cartridges.

Not in my experience. No user visible changes.

There might be some fixes to bugs