I think the erected position is an incredible improvement in safety, you have an unmatched visual and awereness on the euc, and you also have freedom to turn around and look for cars coming from behind and such very easly. On the bike I find to have much less awereness, head low and angled sigh, hands stuck in position, can't look around and spot things as fast as on the euc. Yes the bike is more stable and if you miss a pothole you don't fall... though in the city the real danger are the cars, and you control them better on the euc.
Scooters give you a false sense of control as you can see one for the first time in life and use it immediately... then when you find yourself in a situation that really requires control, you tragically realize you have none. The euc gives you no false sense of control. Scooters are less stable and nimble, can forgive a distraction in EXTREMELY small road imperfections but nothing more, and if you fall the hands are not ready to protect you. The euc for its nature constantly pushes you to be focused and awere, you can't ride passively and you learn it immediately.
The only real con of eucs Is their full reliance on electronics