Pretty good design, very sturdy. Handle could be a little bit bigger, it feels small in my hand. Cracks walnuts well, hazelnuts offer some resistance. Using a little wax based lubricant seems to help.
Personally, I thought that the size of handle was at the upper end of what the nutcracker's aesthetic could handle, but adding an alternative wider/deeper handle shouldn't be too much trouble if that is wanted. How much wider and/or deeper would you want it?
The first few times I used it on some harder nuts, my hand was a bit sore and I blamed it on the handle. However, after waxing the threads and getting the hang of using the cracker, I think ergonomically it’s just fine as is. Great work!