8 or 9 round trip domestic flights packing detectors for me. First one, packed one detector in checked luggage and the CZ6A with batteries removed in the fisher CZ case as a carry on. Going one way, the carry on got a lot of questions but then was OK, coming back not a second look at all. Since then I've packed two detectors and a travel scoop in a checked bag, wrapped in some bubble wrap and clothing. Xcal is actually the only one I bubble wrap, to make sure nothing hits the knobs. I've got a knob guard on the Xcal, but still; if the scoop or coil slide with rough luggage handling, something hard might possibly hit a knob if not wrapped. Batteries removed or disconnected and in the checked bag. Make sure battery terminals can not touch anything that might short them out. I put individual batteries or packs in a zip lock bag by itself. I also take a picture of the packed bag and make an inventory list just in case anything goes missing so that I can document a claim. So far, no issues flying with the detectors.
Good luck to your hunting partner!