What are the advantages of using a 'copper' trowel over stainless steal? Copper is a soft malleable metal, compared to hardened steel. It also produces that green petina (like the statue of liberty). Is that good for plants? Not sure, but they are more expensive. I'm happy with stainless steel.

I haven't used one at all, and although I know there's a biodynamic theory attached to them which persuades slugs and snails to go right on past your plants, surely that effect can't last long? I rarely use a trowel, so I can't think it would be worth the extra price, but for a tool you might use much more often, maybe.

Sounds a bit gimmicky? You'd get a stronger copper effect from sprinkling some pennies over the soil.
No reason not to spend extra for a good, sturdy stainless steel one, get the edge sharpened & some preserving oil for a wooden handle though. It'll last forever!

When they say 'copper' trowel they mean bronze because, as Bathgate says, copper is too soft on its own.

According to a quick search, the reason they are better than steel is that steel leaves a magnetic field behind which attracts snails and slugs.

What a lot of...

I don't think its because it attracts slugs and snails - my understanding is that the use of a copper implement in soil does not interrupt a particular biodynamic field detected by slugs/snails, so they don't stop as they do when other metals are used, they keep on moving past the new planting, simply not noticing the soil's been moved around and tasty snacks have just been planted. The 'copper' trowels are not always bronze - some may be stainless steel or other metals, but coated with copper.
As explanations go, not sure it makes copper particularly valuable other than short term - slugs and snails are forever grazing on the bark of a particular Choisya downstairs in the garden, as well as the young, new stems, and that's been in situ for some years. Not that I realised it was slugs causing the damage, I only found out recently that's likely the cause, and it appears it was - since the application of slug pellets 8 weeks ago, the damage has stopped.

It would be good to hear from anyone who's used copper tools though...

A slug really doesn't care what kind of a trowel you use. Why would you opt for copper over stainless steel for a gardening tool? Is it only aesthetic?