We found the Greentek Gelfree S3 cap first presented by Krisztián Hofstädter in the www.openbci.com forum:
Krisztián Hofstädter has only an EEG signal on 2 channels of his cap. The other channels have no signal and are covered by his head.
Peter Gamma from www.petergamma.org has discussed this cap with Krisztián Hofstädter in the www.openbci.com forum:
https://openbci.com/forum/index.php?p=/discussion/1663/greentek-gelfree-s-eeg-cap/p1
After Peter Gamma showed interest in the cap, most of the videos about it where removed fro Krisztián Hofstädters YouTube channel.
The cap was picked up by the www.openbci.com store for around 700 USD:
Gelfree BCI Electrode Cap Kit
Then the Greentek Gelfree S3 cap was reviewed on the YouTube channel of mBrainTrain:
The demonstration of mBrainTrain shows a functional proof of the Greentek Gelfree S3 cap. But we do not know of convincing proof of function which show of long-term recording of this cap. According to the specifications, the cap can record up to 2 hours continously. But we do not know of manufacturers who would have taken over this cap, or scientists who would have taken over this cap for a long term project.
We mentioned on www.petergamma.org that we miss scientific papers or projects with this cap which demonstrates that it works reliably. And we asked also if this EEG cap cannot be sold alos on Aliexpress.
Then two papers which are not really at the highest level appeared which could not convince us to buy or use this EEG cap.
The cap is now available on Aliexpress for $2,272 USD:
Greentek Gelfree S3 Electrode Hat Ag-AgCl Semi-Dry Saline Based EEG Headset for ERP, BCI and Neurofeedback
https://www.aliexpress.com/i/3256806080854166.html?gatewayAdapt=4itemAdapt
Who buys this cap for $2,272 USD? This is similar to a 32 channel EEG board which was offered first for 700 USD and then increased in price to more than 5 000 USD:
https://www.aliexpress.com/i/3256802367049230.html?gatewayAdapt=4itemAdapt
This is the second example for a product which is mentioned by Peter Gamma from www.petergamma.org:
And after he mentions it, the cap increased in price to $2,272 USD on Aliexpress. Who is ready to pay this price for this cap? Are products like the Greentek S3 given up by the developers and are now usedas demo devices and for stock market speculations and sculping on YouTube, in the web, and on Aliexpress?