Well (avoiding the debate) - Hideous Blow is still a very weak invocation (Eldritch Glaive is much superior). HB still only allows a single attack (since it uses a standard action to activate) and the warlock must be in melee, usually not a good idea for the class. And it vanishes after the attack so the warlock can't use it for any AoO (where Eldritch Glaive specifically states it can be).
So even if the DM allows it not to generate an AoO it is still a very weak invocation.
I agree for the most part, though, for those that don't own Dragon Magic... it is the only melee alternative, besides invoking defensively a standard blast.