As with other reviews already briefly noted: in exchange of the key bit MUST the original, as well as at the key bit Replacement Housing replaced. THIS IS with a pin secured knocked out, OR Then of course, carefully re-MOUNTED TO BE.
Without tool that is not possible!
With some craftsmanship and a extra pair of hands, that's no problem.
For a better understanding, I've added a photo that clearly shows the pen (and the key bit blank of the new key, and our old base with the broken push-button).
How long does the complete replacement housing will keep now remains to be seen, but as we now know how easy it is to replace the complete housing, I can live with that, if this case 5 will not reach 10 years lifetime.
4 Stars for the price, because it does what it should and not much worse than the original (that is also not high, the hammer).