Code review comment for lp:~a-j-buxton/phablet-tools/download-only

24 + '--download',

Would you mind using --download-only instead? This is just to make it easier for people when only reading the arg list.

37 - device = validate_device(adb, args.device)
38 + if args.download:
39 + device = detect_device(adb, args.device)
40 + else:
41 + device = validate_device(adb, args.device)

I'd suggest to always call detect_device and remove it from validate_device. Also move validate_device a bit bellow in the code, to call it only in case we're actually flashing the device (bellow line 59, for example).