Hey everyone just an update.
I bought a new Tesoro Compadre from Lost Treasures a while back. I had a good look at the second hand ones on the US ebay, however the current exchange rate didn't really make it worthwhile, but I would definitely consider it for the more premium range of Tesoros where the savings would be greater.
I have just been testing it around the house and local area, so far I have found a nice assortment of bottle tops (and 1970s glass), some chunks of aluminum and some rusty nails. It surprises me at times as to how sensitive it is.
One interesting thing I've found is that it picks up interference at times and starts beeping at a constant frequency, we live near an airport so I think it might be picking up a radar signal or similar?
The only thing I dislike is it's lack of volume control. When playing through the speaker it's super loud (fighter jet/black sabbath concert loud). I plug in headphones and just leave them hanging on the handle, you can hear them easily, but you would quickly go deaf if you put them on. In the long term I might get some headphones with built in volume control.
But in short it is a very impressive detector and I'm very happy with it...