The test results go-rebels points you to are a little hard on the Shadow. The build quality is far better than the Tesoro, its lighter, rainproof and does better over the whole conductivity range than the Tejon. Drawbacks are you have a more limited range of coils and in heavy iron in needs the seven inch coil fitted. Finds anthracite far deeper than most machines. The discrimination control is more suitable for the U.S. than Europe. You have a sort of click point as you turn the knob. A fraction below this point and your digging iron, a fraction above and you miss the small/thin European hammered silver.
Sensitivity to small items is good and it copes with mineralisation in my area but not extreme mineralisation.
There's the new Troy due out about now. Hopefully this will mean that you will still be able to get repairs on the X3 and X5. Coil covers in Europe are in short supply. If they use the same moulds for the new machines coils to save on costs that will solve that problem.
You really need to try both in your area to see which you get on better with. Try and get hold of the Vaquero as well as it can be hyper tuned to the performance of the Tejon or left as is which seems to better suit some sites.