I haven’t tried any of these almost-DIY generators so I can’t speak to them directly. That having been said, I have used for the past 7 years the Acoustic Revive RR-777 which is a Schumann ultra low frequency generator. I find the device’s effects to be subtle but still noticeable. To me the main area that’s enhanced is the sound stage – it becomes more spacious with a better separation of the instruments.
Here’s a review from Positive Feedback magazine: RR-777