They are USB 3.0 and do support fast charging if using an adaptive fast charger and/or battery pack that supports fast charging only. If using a normal battery pack or regular adapter, it will charge like any other device. It will not do any fast charging if connected to an USB 3.0 port on a computer either (tested my Surface Pro 2; I never expected it to as it doesn't have enough power from the port to do so). However, it does have USB 3.0 transfer speeds connecting to a USB 3.0 port. Transfer speeds of course will vary based on the hardware you are using. It is considerably slower when transferring to/from an external SD card within the phone. Again, due to hardware/software limitations and protocols used. I have not tested it on any USB 2.0 ports. But there should be no issues as it will step down to what USB 2.0 can handle (as with any other USB 3.0 device on USB 2.0 and vice versa).
These cords are braided and feel very durable. The silver connectors are indeed metal and they will warm up with use. The cables are also rigid, but are somewhat flexible which adds to what should make them very durable. They are also much thicker than the OEM cable provided by Samsung. Overall, I am quite impressed with them and expect them to last me a good while.