1. Easy to view & remember.
2. The oil smear is visible in reflected light, and that pattern is not quickly overwritten by using the device.
3. Typical gesture patterns mean gestures start from similar positions (high) and are frequently unoriginal.
4. Gestures are simpler than the equivalent code (e.g. the passcodes 1397 and 1235987 are gesturally identical)
5. In practice the reality of finger sizes mean that join-the-dots encourages users to draw a gesture using only adjacent dots (e.g. connecting dot 1 to 2, 4 or 5, rather than 1 to 6 or 8.)