A bio trigger fires on trigger pull and fires again on trigger release.
A $450 dollar bio trigger can fire on pull, hold the trigger back ( don't realese ) move the selector to semi or safe, release the trigger and not fire the second round.
With the home made, that's not possible.
The only way to not fire on release is to keep trigger to rear, drop mag, and eject round from the chamber. I've never not wanted to fire second round, but I practice the procedure sometimes so it will be second nature in case it should ever come up.
TO MAKE A BIO TRIGGER is simple
File end of disconnector so hammer will release before trigger bar can ingage notch on bottom of hammer, but not so much that the hammer won't catch at all on disconnector.
That click you hear when you hold the trigger back after a shot, then release slowly is the hammer bar catching in that notch after the disconnector releases.
You need to remember that once you do this, that is what it always will be. The only way back is with a new disconnect or. I have a lower with that setup in it. I can pop two pins and switch back.