I can't say if they're cheap, or efficient. They're cheap for some and efficient for others.
As for myself, I don't see them as any of those.
I consider Dead Angles a glitch. I came to this conclusion thanks to actually hearing the impact the weapon does on the shield, yet it still does damage. You don't hear this sound when you use Shotel. Also, Dead Angles doesn't work in PvE, thus it's probably something created by the poorly balanced PvP mechanics. The fact if Dead Angles actually are a glitch, or no is pointless to me. I'm talking from my perspective, which will not change, even if From comes and says Dead Angles are intentional. In my eyes, it will remain a glitch no matter what.
The most common argument people use to justify Dead Angle usage is "I use DAs to fight turtles." You see, to me, using that argument is exactly like saying "I suck at PvP and have to resort to using glitches". I don't have a problem with people that turtle, or use shields for what they are meant to be used. Blocking.
Shotel, Black Flame, two handing, kicking, AUX, spells, there's so many ways to deal with somebody who is overly attched to his shield. Thus I don't see how anyone can have a problem with turtling so severe they have to resort to using glitches. I mean, if it's boring for you to fight turtles, Black Crystal, suicide, or disconnect.
The second most common argument is "It's a good counter against parrying."
So is kicking. Can't kick with your weapon? It's probably for a reason. Use different weapon maybe? You can always use spells, or just plain and simple backstab the guy as he parries. C'mon...
In my opinion, Dead Angles are the same kind of glitch as TWoD (buffed Stone Greatsword R2) and other similar glitches. As such I treat Deand Angle users as glitchers, or hackers and have a nice stock of 90+ Mushrooms and Divine Blessing for anyone that uses them on me in random PvP. If that fails, pulling the plug and kicking the person into my Block List takes only a few seconds.
PS: Lollipop to the first guy that doesn't understand what the word opinion means and will ask me to prove Dead Angles are a glitch.