The question you've got to ask yourself is, do you want these cameras to act purely as a deterrent, or would you require footage to be played back at any time??
If you want them purely for a deterrent, make sure you put the dummy cameras where they can be seen and put up signs indicating the presence of CCTV.
If you do want them for playback purposes, I'd recommend getting your system hard wired.
Sorry I can't advise on the quality of the dummy cameras, we've got a 4 camera system, which is hard wired, so I haven't seen the dummy ones :(