Ive heard about this before, didnt give it much thought. But i had some bamboo set up in my pots to protect my seedlings from asshole squirrels - and a little piece of copper wire lying around, so i put them together in 1 of the pots.
I started the 2 seeds at the same time, same seed batch, same mix, fertalizer, pots, etc...

And the 1 with the copper spike is a monster, really outperforming the other.
I know there are lots of normal reasons that 1 seed from the same batch could do better than another - and if I wanted to be scientific about it Id have to repeat it a bunch of times.

But, has anyone else tried this? Any other direct experience?
(Copper wire seedling on the left