I think it comes down to the fact that the machine doesn't make bottles the way the formula manufacturers advise making them. Basically, formula manufacturers can't guarantee powdered formula is safe unless it's sterilised in nearly boiling water. These machines shoot in a hot shot of water, but then immediately top up with cold water in order to bring the overall temperature to a safe drinking temp. Is this how lots of people make formula by hand anyway? Yes. Is it how it's supposed to be made? No. There just is no guarantee that a shot of hot water for a few seconds is enough to kill the bacteria in the formula. From a food hygiene standpoint, it very likely needs more time than that (but there's no evidence anyone has actually studied that, maybe the formula companies have? but they don't claim to). When you make formula with nearly boiling water, and then take several minutes to cool it, it's probably enough time to sterilise it. When it gets cooled immediately with cold (even if boiled) water, it probably doesn't. I think that is the concern. Now does it matter? Maybe not. Many people do make bottles by adding hot water and then topping up with cold. If you're going to do that anyway, you might has well have a machine to make life easier, right? But at the same time, I think they want people to understand that it could be a risk. If you did happened to get a contaminated batch of formula, this might not do enough to sterilise it and there is still a risk baby could get sick. But I think most people who use the topping up with cold water method understand this already (or at least they should), so if it's what you're comfortable with, then it's a great way to make things easier. I didn't use one of these with my first as they didn't exist back then, but if I formula fed the next time around, I probably would, assuming I had a healthy baby.
I'm a bit confused as to how they can sell them if they're not safe and am now also worried incase I've made dd ill. 
