I don't think he branded the entire escape system was 'utterly useless', just the 'safety pin mechanism' - which has been shown (sometimes) not to render the system safe, even when fitted (albeit incorrectly).
However, the pin usefulness is a slight red herring as the pin would have been removed and stowed by that stage - as mentioned previously.
The significance of 'likely to mislead' is that anyone seeing the pin fitted (albeit incorrectly) would assume that the handle was fully in and therefore fairly safe. It has been shown that it can in fact be partially dislodged and in a fairly precarious condition.