Earlier quoted context omitted.
This is dangerous, as you aren't signaling people behind you if you are braking... Edit: I would likely soften the "dangerous" wording above. I'm not trying to claim this is guaranteed to get you killed. Just pointing out that bypassing a well established signaling mechanism of your vehicle should be a deliberate act. Not one of convenience.
Engine breaking just means slowing down by letting the foot off the gas. You aren't really slowing down that quickly. Someone has to really not be paying attention to miss it. It would be the equivalent of someone merging.
Given how often I've driven on stretches of road where engine braking is prohibited, I beg to differ.
Engine braking is usually braking by shifting to a lower gear.