The idea is that they form an electric cell with the slime under the slug and give it an shock. So yes they work.

I find they are very good until the plant grows up and spreads out and touches other plants providing the little beasties a way in.

Yes, they do - I've just bought another batch for my garden. Look at my recent photos, there's a trillium in flower, untouched.

I work in a botanic garden and yes they do work. They need to be at least 2 inches thick and any foliage needs to be trimmed from the ground else slugs get in that way. They do nothing for other garden pests such as vine weevil, caterpillars etc, s bear that in mind.

I have a load of them in my woodlandy patch near the back window, but the husband disapproves. After everything had died down for the winter he said he was left looking at a graveyard for cake-tins...