QED tips.
One feature of the QED that I have found useful occurs when a target has been dug and is in the heap of material removed from the hole.
It has always been my habit to lay the detector near the heap on its side, with the coil in a vertical position. It is easy to wave handfuls of dirt past the coil to identify the target, however various types of popular detector brands have such a problem with EMI that spurious sounds make this an arduous and difficult task. This can be remedied by laying the coil flat, parallel with the ground, and maybe using a plastic scoop, but this is not as convenient as just waving a suspect handful of dirt past the vertical coil. The QED, because of its better resistance to EMI, makes identifying a target once dug, quicker and easier.
The type of coil you choose to use on a QED is a matter of personal preference, and as long as you use a ML PI compatible Mono coil, it will work just fine. There are many after market coils of various shapes and sizes to choose from, and the advantage of the QED is that you can adjust the detector settings to get the best out of your choice of coils from very small coils for finding tiny pieces, up to extremely large coils for those lager deeper nuggets. The QED has the power to operate a wide range of coils, and when you opt for a large coil, get ready to dig some pretty serious holes. (don't forget to back fill them)
Going cordless with the QED is easy, and not necessarily expensive. ML and Garrett produce cordless systems , but they are not cheap. There are a number of options, and I have covered these in previous posts.
As far as second hand QEDs being on the market. There are all sorts of s/h detectors on the market, as people sell them for all sorts of reasons. A s/h QED presents an opportunity to pick up a very good machine at a reduced price.