The data quality of wearables to detect sleep stages is in the 90%+ accuracy range now. Which is near what polysomnographers score at - nobody completely agrees on what stage is what, there is always deviation. Wearables are definitely good enough at this stage.

Zeo is not the only consumer EEG either, though all the current headbands (including what we are building at https://affectablesleep.com) have some sort of sleep stimulation at it's core.

Frenzband I believe is shipping, I haven't tried one, and don't know anyone who has. We have a Somnee at the office, and it is unbearably painful to wear. I'm highly skeptical of the "science" of either of these devices as well.