Python Constraints

I’d like to create constraints in GE and, as far as I can see, the constraints in GE are from Bullet’s Python API.
So I was just wondering if I add my own constraint (for example, Copy Location) using Python for an Armature of 20 bones for every bone than would the performance of the game executable fall from this a lot? (This means, that on every frame the location of every bone has to be read from the source and set to the destination, seems to be a bit tough, especially as for Python).