I agree with you that they look nice on finish joinery, and when I
know I have to take the time to get each one set exactly right
(probably by hand) - but for situations where I would expect to drive
them in flush, or to take them out again, I found chewed heads or even
snapped threads happened too often, i.e. even a quite rare breakage
will take up a chunk of time to put right - when compared to no time
wasted on breakages with spax.