Re. safety pins, I've used them in all sorts of situations and never known one to accidentally fall off but mine went missing on my recent trip.
I though I would get away with the plastic coated metal ties but no matter how many times I twisted one it pulled apart easily when I pulled on the zips.
I'm not bothered about security, I just don't want all my clothes to fall out but use something that is easy to get off at the other end.