Sorry for the late response. Two main reasons. Firstly, I wanted a waterproof pump as I swim a lot, and secondly I wanted a pump with integrated CGM (having been converted by the Libre). It was then down to a choice of the 640G or a Vibe. I don't know what swung it for the 640G in the end, but I have no regrets. The only tiny niggle I have with it is that the belt clip keeps it oriented 'portrait' rather then 'landscape' which can be a bit uncomfortable. Most of the time though, I just drop it in my pocket. And, it does alarm a lot, especially with CGM. I should turn most of them off really.