Sorry, maybe you're right and it's wrong to say that they are exactly same, because UCL brakes both front wheels ("bremst beim Untersteuern beide Vorderräder"), but the EUC system in the Corsa can apply braking to all wheels when necessary, so it's safe to say it's the much more developed version of UCL, as its name ("Enhanced") implies.
Therefore, it is also wrong to say that Corsa's ESP system doesn't have Understeer Control.
oh, "more sorry" of my opinion, I rode too fast over all, becaus I thought you compare between EUC / TCPlus !
It's OK. 
The important thing is that our lovely Corsas have a good ESP system :auto:
and I have to look in winter about the performance of my Meriva-ESP, UCL / EUC....I don´t know.
On real street-situation you can´t trust to full-speed contolled by ESP-X, because the Middle-Line in separation to the oncoming traffic is too small for gamble to the one life !
You're right. The driver assistance systems are just meant to take over and help when driver can't respond fast enough and lose control in unavoidable situations, they aren't for to show off pushing the car over its limits on public streets!..
