SOMA Quantum Ocean

Ok, so this isn't for everyone, but if you're reading this you are at least a little curious.
First, build quality. As with everything from Soma this is really solidly and well made outside and in. (You need to open the back to fit the battery, so I know the actual electronics are really well put together.)
Then, sound quality. Again, excellent. Wide spectrum sound. The volume knob is smooth and quiet (ie no crackles or brush noise) - you can get a really smooth fade to nothing when you finish a session.
Third, function. Well, there's the obvious use as a device for meditation, which is well covered in the accompanying manual, and which I'm finding very useful. You could also use it as a preparation for sleep; just listening to it (on headphones ) for 20-30 minutes before putting your head down should help you drift off more quickly (mainly because I find that it quiets thoughts down).
Another aspect of the way you use this, especially the first exercise, is that it trains your ability to focus your hearing. The first thing you are training is your ability to "listen in to" the sound, to focus on the different layers of, and the other sounds within, the broader white noise. As well as improving your general ability to focus your attention aurally, and stay in that state for longer times, I think this would improve your ability to listen in to the details of a mix and stay focussed on what any particular instrument is doing.
And there are probably other benefits as well.
I'm very happy with mine!