*sigh*
This case is aluminum, and as the OP states, it will dent when dropped from a good height.
Realistically the worst drops i've ever had happen with a little forced behind them too; trying to grasp the phone resulting in me slapping it away, or if i have brushed the phone off my lap or table on accident.
This is definitely not equivalent to an otterbox.
Also, the 2nd mic is for noise cancelling. Using the speakerphone has no relation to it. you're still talking into the mic(s). people have reported echoing effects when the 2nd mic is covered.
JMHO. do what you want, but that looks like a rip off. I've read bad things about this case.
EDIT: also, unless you go with some ebay cases, most of them (OEM, Verizon, Seidio..etc) are a rubberized hard plastic. They don't "shatter".