I don't think it's so much colic or reflux, it's more a concern about them being unsterile. It's just that they don't actually make the formula according the manufacturer's instructions, which means they don't sterilise the formula itself. It's nothing to do with cleaning it, just that formula itself in powder form can harbour bacteria that can make babies sick if it isn't sterilised properly with near boiling water. The perfect prep's aren't actually designed to do this and maintain the formula at a temp that will kill the bacteria (the shot of hot water at the start doesn't do it because it doesn't hold the formula at a high temp long enough before adding the cold water). Now that's not to say that it will definitely cause any harm. Most people probably make formula like that themselves just using a kettle, but it does say on the formula packet not to do that. If you'd be making formula that way anyway, carry on and don't stress about it (just be careful about using up a packet you open in the time it says and use clean hands and scoops every time you're handling it to minimise contamination). But NHS midwives, health visitors, etc. have been asked to warn people who don't know it's a contamination risk, because actually I don't think most people realise that it doesn't actually make it correctly according to the manufacturer's safety instructions.
