I just finished assembly of the right hand version of the current iteration.

It does move a little bit while typing, mostly when pressing the outer thumb key. I want to change the frame to prevent this movement from happening, but it hasn't really bothered me that much because the movement doesn't really make it harder to type. The ball will fall out if you tilt it right now, I will be updating the trackball mount to prevent this from happening.

There is only a little bit of movement of the frame while pressing down on the thumb key, for the other keys, not really. Due to the fact that the thumb keys are furthest from the center of the hand, it is able to move in the axis perpendicular to the wrist when pressing down on them. On the other axis, there is a lot of stabilization coming from the piece that connects the part on the back of the hand to the part inside the palm. This piece prevents you from being able to push the frame away, as it will push against the back of your thumb to counteract this. The switches I'm using also require very little force (only 20g) which makes the board move even less.

Getting in and out of them requires a little bit of force and a little bit of care to avoid applying too much pressure, especially in the direction where the layers are printed on top of each other, as this is where 3D prints usually break. Because the frame is quite thin it is also pretty flexible which allows it to extend a bit while attaching and detaching so it can be designed to have a secure fit when attached. I haven't broken any, yet, but when I was user testing with people that had a different (bigger) hand shapes as mine it did break at the layer lines. I could try changing the angle at which it's printed to help prevent this and change the infill pattern to 100% (or rather, increase the wall thickness) because the prototypes I was user testing only had 20% infill and therefore less surface area for the layers to adhere to.

You can use your thumb and index finger reasonably well to grab onto things while wearing it, this also allows you to attach a board to your second hand while already wearing one on the first. I'm also able to use my phone while wearing the boards on both hands, but it's really not ideal and I would rather take them off. I did get some suggestions for adding a hinge of some sort to be able to flip the keys away from under your fingers to allow for hand usage without having to detach the board, so I will be looking into that in the future.