Hi Dan,
That is just a piece of scrap MDF I used for testing.
There are quite a few problems associated with using an axis direction pin which crop up from time to time and eventually become a real pain.
As mentioned earlier the software polled EStop does not change the state of a direction pin but it can turn off an output thus using an output gives an added safety feature.
Feed hold, if it ever has to be used, creates another issue when motion stops with the laser still on - easier to handle an output than a direction pin here.
My B axis DRO can, in error, somehow get to a -1 step position then the B0 command that is supposed to turn the laser off actually turns it on - another B0 command does nothing to turn the laser off - only the separate commands B1 and B0 will turn the laser off.
At initial power up the state of an axis direction pin is not always guaranteed.
There are a few other issues as well so overall using an output for switching is far far preferable.
Tweakie.