BubblHandz® - Midnight Black Piano Hand Posture Trainer

Very useful

Took me a second to calibrate but totally changed the trajectory of my playing and posture.

They're great as long as you don't go past the first 5 fingers. Once you tuck your thumb under the bar gets in the way. The idea is great, but it definitely has some flaws

They are comfortable and easy to wear. And they effectively remind me to keep my hands in the correct position.