Summary

I liked the design of my previous stand, but it just wasn't stable enough.
Using the hinge from thing:4128774 and the shape of thing:1032038 results in a smaller, more stable stand.

Note that this is not one size fits all stand, you need to set openwidth and slotwidth and probably tableth to best fit your device. Openwidth should be slightly narrower than the device. slotwidth should be a few mm thicker that your device. tableth is used to calculate the center of gravity of the device so that the legs are long enough to keep it from tipping over. The default is to make it 5% larger than perfect for extra stability.

I have included default STLs for a small tablet and a medium size phone.
If you'd like me to include an STL for your specific device, leave a comment with the three dimensions above and the device name and I'll add it. (Or customize it yourself.)

This thing is unfinished, but it's been sitting here unpublished long enough.
This really needs a slop compensation adjustment to allow a wider slot but then adjust the degree angle to make up for the extra space, but I haven't had time to add this. It can be manually done with some care. I may eventually get to it.