Well, I've spent some time with this, and I get a different result that the posters above.
Regardless of the app (bxactions or Bixby Remapper), the apps won't work unless Bixby is setup and left on, with the Bixby button enabled. If I disable the app, or leave the app enabled but disable the button, neither apps work.
When they do work, they work in an identical fashion. I push the button, a Bixby event is obviously caught by the app, and the app rushes to display the "remapped" app instead. In that initial second or so, Bixby is displayed. Sometimes it's just the "Bixby bubbles" display.
Either way, I am left with something that looks like I coded it up in 60 seconds myself. Sort of like a kludge. Very obvious that it's catching an event and trying to trick the user. I am just not feeling it.
I've run through every iteration of installing these apps with Bixby fully enabled, disabled, enabled with the button disabled, you name it. Just not getting a polished result.
I'll try BK Disabler next. Chances are, it endeavors to catch the button press event, just like the other apps, its a typical technique. But, maybe that will work better on my N8. I'll try that when I get the time.