the cable is a standard high speed HDMI cable. It simply transfers 1s and 0s.
do you power the mhl from a usb port or AC power? you will get different current ratings depending on which one you choose.
I am not sure if the one has MHL spec 1 or 2. if no one can provide that answer, perhaps ask HTC directly.
Nowadays with choromecast and medialink (wireless technologies), not many people are using MHL or even know what it is.
I can tell you this though, no matter which mhl spec this phone has, if you use the phone for other CPU intensive activities (web surf, etc.) at the same time you are viewing movies, you are certain to run out of power.
the phone will not allow much current to "keep up" with your activities, as you are asking for trouble... as in HEAT. heat damages the lithium ion cells and causes the cell environment to become unstable. if this occurs, the phone will cease to charge and you will be right back to square one.
bottom line, in my opinion (others will also chime in here as well), if you want to use mhl, try to keep other activities to a minimum.