Yes its flexible, problem with hard shells (well for me) is that over time they start to scratch your device.
I haven't used them on any of my devices since my Nokia 5800, like to keep my devices, as close to new as I can, can't stand chips and scratches especially from something that's suppose to protect it.
The link you posted above has a wrong description, its definitely not a hard shell.
There's only 2 types of original cases as far as I know.
Here's the original desire c hard shell which comes in 2 colours:http://www.amazon.co.uk/dp/B008AJA1C..._am_gb?ie=UTF8
Sent from my HTC One X
HTC Wildfire S s-off running cm9
HTC Sensation s-off running cm10.1
HTC Desire C DeSensed running @828MHz
HTC One X running fully stock, waiting for sense5