Hi.
They are very useful TBH - I hate taking gravity readings, but more importantly you can see with the shape of the graph how the ferment is progressing and if it is stalling. Also useful for doing a Diacytyl rest if you are at the last ~5 gravity points of a lager.
They can be a little bit fickle as devices however, as mine is being at the moment, but work great when working. Good wifi where you ferment is also a necessity for connectivity.