I would prefer vials any day, but if you have sterile vials and keep everything clean, including sterilze the sachet before opening it, it shouldn't be a problem. I have used them once and they worked just fine, just like any other high quality gear. And just like any other gear, it will depend on how clean the gear is to begin with. I once used a few sachets from naps, and they were good. The gear was thin and painless, much like Geneza. just be extra sure that your hands and everything involved is very clean during the transfer process!