Article from AnandTech says it takes
200 minutes to mill each HTC Aluminum case:
The HTC One Review
AnandTech | The HTC One Review
HTC begins construction of the One from a solid piece of aluminum. Two hundred minutes of CNC cuts later, a finished One chassis emerges. Plastic gets injected into the chassis between cuts during machining for the antenna bands and side of the case, which also gets machined. The result is HTC?s ?zero-gap? construction which ? as the name implies ? really has no gaps between aluminum and polymer at all for those unibody parts. There?s no matching parts together from different cuts to achieve an optimal fit, everything in the main chassis is cut as one solid unit. It?s the kind of manufacturing story that previously only the likes of Apple could lay claim to, and the HTC One is really the first Android device which reaches the level of construction quality previously owned almost entirely by the iPhone.
Imagine the number of CNC milling machines required if Samsung chose to go this route. I doubt HTC will come close to the number of S4's sold worldwide.
IFixit.com says repairing the HTC One is essentially not possible without great difficulty and possible damage to the back of the aluminum case.
HTC One Teardown
HTC One Teardown - iFixit
Very, very difficult (possibly impossible?) to open the device without damaging the rear case. This makes every component extremely difficult to replace.
The battery is buried beneath the motherboard and adhered to the midframe, hindering its replacement.
The display assembly cannot be replaced without removing the rear case?this will make the most common repair, a damaged screen, nearly impossible.
Copper shielding on many components is difficult to remove and replace.
I have several family members who brag about their iPhone metal cases. Then I look and they have them buried beneath an Otterbox ....ha!! Plastic has worked for me! Getting very anxious for Verizon to begin selling the plastic S4 !!