How useful could something like this be for research? I'm not a neuroscientist so I have no clue, but it seems like the only justification I can think of..

The general idea of an EEG system that posts data to a network?

Very, but there are already tons of them at lots of different price, quality, openness levels. A lot of manufacturers have their own protocols; there are also quasi/standards like Lab Streaming Layer for connecting to a hodgepodge of devices.

This particular data?

Probably not so useful. While it’s easy to get something out of an EEG set, it takes some work to get good quality data that’s not riddled with noise (mains hum, muscle artifacts, blinks, etc). Plus, brain waves on their own aren’t particularly interesting—-it’s seeing how they change in response to some external or internal event that tells us about the brain.

Not a neuroscientist either but I would imagine that raw data without personal information would not be useful for much. I can imagine that it would be quite valuable if accompanied with personal data plus user reports about how they slept each night, what they dreamed about if anything, whether it was positive dreams or nightmares etc. And I think quite a few people wouldn’t mind sharing all of that in the name of science, but in this case they don’t seem to have even tried to ask.

If they're taking patient data for research without permission, they are not ethical researchers.

I believe they use it for sleep tracking