The band dimensions are 140-240mm (5.5 - 9.4 in). The sensor dimensions are H,W,D - 57.4 x 35.2 х 18 mm.
Our tech team were able to integrate a great amount of useful features into the band, so it may seem a bit bulky at first indeed. However, most of our customers report that normally they quickly get used to the size of the device and do not feel any discomfort.