Originally Posted by Mr. Dent
While I'm sure he is okay, he is not Quicksilver. Them casting him just proves he will be little more than a glorified cameo and Singer is only interested in using Quicksilver's abilities on screen, not really the character itself. That "before he was an Avenger he was just a really fast kid" comment supports this as well.
I've only seen him in The Office and Kick Ass. Both fairly small roles, but he was essentially a spoiled brat and/or sarcastic dick in both. I see no reason why "he is not Quicksilver." But I will find another instance of his acting skill to confirm or deny.