MyTouch:
in OS X it works like a mouse. It's having a fixed orientation to the
screen position. So if you paint a dot on the paper, when take the pen
away & later you come back to the position of the dot, you are also on
the same position on the screen. This makes sense for painting.
in OS X at the moment the receiver can only be used at the middle top
of the paper (not at the left or right corner). It would be better if
they would implement a way to make left & right corner also possible.
The tip of the pen needs to be always visible to the receiver.
Depending on how you hold your hand, your hand can block this. So in
most cases for a left handed person the right corner is a better
position for the receiver. For right handed, it is the left corner.
Independent from the OS:
It's good for painting things which you can't paint with a mouse. Like
a freehand circle. It seems to have no sense for the amount of
pressure. So it is only differencing writing or not writing. The
resolution is OK, but may be it could be better. The pen needs 2
Button cell Batteries. I don't know how long they will last. However,
after 30s not writing, or pressing the key, it goes into sleep. So i
hope it will work for a while.
All in all it is a good usable painting device without pressure amount
recognition!