[shkkmo]

On a self balacing PEV, if the motor decelerates on it's own (without a weight shift from the rider), the resulting weight shift will not be gradual. You might tip forward slightly slower in comparison but the nose dive would still happen pretty much immediately. This is because in order to maintain speed, the CoM must be in front of the balance point.

The design of self-balancing PEVs isn't fundentally unsafe, but it (like most sports and means of transportation) does carry risks that you should be aware of and compensate for.