The couple I saw had all the deflection they needed. Never saw anything suggesting any kind of limitation. Nor have I read that any of the WWII aircraft that used them had any limitations. MOF they retrofitted them on one airplane to boost the response. Might be where the nickname came from?

If I remember correctly, the paper I read about them some years back implied their performance was a function of their location within and proportion to the driven surface, that it was possible to have them too small. But I do remember the paper leaving out how to tell they were big enough.