Fumoto valve male threads will, in most instances, be longer than the female threads in the oil pan. Because of this, you will likely have a little more oil left over in changes.
We've had a handful of users test out the difference between the two. To their measure, whatever is left in the pan isn't noticeable enough for them discern between an oil drop with or without our valves.
If you're worried about leftover particles, please keep in mind that warming up the engine properly before doing your oil change should put particles in suspension, making it easy for them to escape once the release on the valve is triggered.
Keep in mind, in many instances, the pan shape itself will not allow for every drop to escape.