I got a handheld sudoku machine for Christmas. It was made by TechnoSource. It will be returned. Here is a short list of shortcomings.
1) Puzzles are not symmetrical.
2) Screen very hard to read in any light.
3) No way to insert pencil-marks.
and the coffin-nail...
4) Puzzles do not have unique solutions.
I enjoy doing puzzles with pen and paper, and I don't think any $20 piece of China's finest technology will change that.
QP