The necessity to carry a separate physical object is the primary drawback. Users typically carry a mobile phone, keys, and a wallet; adding a banking token introduces bulk. Furthermore, scenarios such as a drained battery (in older LCD models), a lost device, or simply leaving the key at home result in a complete lockout from financial services.
If the screen goes blank and pressing the button does nothing, try holding the button for 5 seconds. Still dead? Request a new key. hsbc physical secure key