Review (5/5): Worked well with my HTC One M8 and reliably using Anker's own charging cable; a DROK multimeter is recommended
I did extensive tests on charging my HTC One M8 with various combinations of this Anker Power+ 3-port USB charger, HTC's fast charger, both support Quick Charge 2.0, and charging cables from Anker, HTC and PortaPow. In order to monitor the actual charging voltage and current I also inserted a USB multimeter from two sources. In all combinations an optimal output of 9V/1.3A (~11.7W) could be reached, but not always. It turns out the quality of charging calbe and the multimeter matter a lot. A DROK USB 2.0 multimeter worked reliably so as Anker's charging cable with a regular optimal output. Anker's charging cable appears quite durable with bending. However, any cable with constant bending and folding would have a limited lifetime resulting in lowered output current and voltage unnoticed, so I would recommend insert a higher quality USB multimeter as well. On the other two regular USB ports with IQ technology an optimal output of 5.2V/1.5A (~7.8W) was reached. In my original testing not satisfactory result was obtained; Anker customer service nicely sent me their own brand charging cable for continuing more thorough tests.