Lots of people have taken issue with the trisaber lightsaber that appeared in the trailer for Star Wars: The Force Awakens. People said it was ridiculous and would never work, while others came to its defense—Stephen Colbert being chief among them.
See Also: 3D Print Your Own Trisaber
YouTuber Thrand made a mock-up of the lightsaber and demonstrated (pretty convincing) how it could actually work very well. He even made a follow-up based on comments to more clearly demonstrate potential damage. If this doesn’t convince you, then nothing ever will.
See the video after the break.