Like drgonzo2k2, a significant drop in gravity reading ALWAYS happen when cold crashing. I don't understand why the development team insists that temperature has no effect on the gravity measurement, as it certainly does in practice. Every single time.
So basically, this little gadget cannot replace a real gravity measurement, if you want to know an exact FG. What I find it useful for, though, is a close monitoring of the fermentation. With this gadget, it is super easy to follow a "quick lager" method, for example: you can time your ferm temp schedule based on where the fermentation is at in reality (not after x amount of time). So I can start raising the temp after 50% of the fermentation, for example, to ensure good attenuation. It worked very well in that regards.
Besides the incorrect FG when changing temperature, I found the battery life to be very annoying. It almost looks like I need a new battery every month. On my last batch, the battery died after 2 days of fermentation. I think I may have left it open my mistake (left it "up", instead of upside down). I wish there was a way to know for sure when it's sleeping, and a battery level indicator in the app.
That said, the team has been very helpful: they sent me 2 replacements so far (the first was having very incorrect readings, and the second seemed to go through batteries within a few days).