Yes I have and I would highly recommend it. I used one in university as a subject so I have only done it the one time. My thoughts and observations: 1. It is an intense introspective experience so if you have going through something in your life like your wife cheating on you or you murdered someone then I probably wouldn't recommend it. I spent a lot of time daydreaming about the future and thinking about recent fuck-ups. Which was disappointing since I could do that any day, I wish I was more in the zone. 2. Condensation builds up in the tank and then drips, which was super fucking annoying. It is super quiet so the drip sounds so loud. Plus you are not moving so you actually feel the drip hitting the water. 3. You start to get phantom itches after awhile and those are annoying but it went away after a while of not really moving around. 4. I answered survey questions afterwards, they told me what they were testing for but I don't remember the details as it wasn't particularly interesting. Overall I would recommend it if you have a shot, I have no idea how much these types of things cost.
That's pretty cool to do it for research. Probably a stress related thing. I actually have used them a lot, just made this to see other people's opinions of them. The dripping can easily be resolved. I am building a tank at the moment (improving on my last unfinished build, really) and making a slanted roof so the condensation on the roof rolls down to the wall and doesn't splash down. It's crazy how aware you are though, with feeling such a small amount of water movement. I even feel my heart/pulse moving the water when I'm really, really relaxed. If anyone else is interested in cost, it's usually anywhere from $30 - 60 an hour. $30 - 40 is a good price IMO. Owning is a whole other deal. DIY builds can be done for under $2000. Commercial tanks sell for $8000 - 100,000