The Mediflow already bulkier than my pillow (Bugatti with hollow fibers) without water so I have time only filled the minimum recommended 2 liters. Unfavorable case, the system is how to get the air out of the chamber - you're never sure if you caught anything, and there is always a small residual returns (the more difficult the less water you use) - better would be a system with overflow at the you then definitely no air has in it.
The film of the water chamber also leaves a bad feeling, the material looks more like a normal plastic bag because a stable plastic.
Conditional principle disadvantage is of course the very high weight when full, which makes the pillow very unwieldy.
The first feeling with the pillow was ok, the filling evenly seems pleasantly soft but the head is when the shoulders sink as intended in the mattress felt a bit high.
Prone I felt very uncomfortable because the neck is too pushed backwards.
The result after sleeping in the supine position was then mainly very sobering, tense neck and shoulder area where I have no problems with my old pillows. Take even less water is not an option because then the effect of the water chamber is not or hardly relevant.
The cushion is like nothing more for people who have a mattress in the already sinking shoulders and well or rather flatter pillow.