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I've been riding XT Di2 for the past 5 months and that hasn't been my experience. Zero dropped chains and I just run an upper guide (always have). Shifts flawlessly. As far as chain slap noise it seems to be heavily dependent on the bike and what kind of chainstay protection it has, my HD6 is fine. Even the most vocal critics (Pinkbike tech editors) have noted that it varies from bike to bike. Not trying to convince anyone that they need to buy it, just relating my personal experience.