HTC, for a long time, resisted the outburst from the 3rd party dev scene. However, the company had to give in to the rising demand for phones that could be modded, and is now making business out of it.
Today saw the launch of not only the ‘regular’ HTC One (M8), but also the Developer Edition of the device. The One (M8) comes with HTC’s Sense 6.0 UI atop Android, which is also modded by the carrier to its liking. However, if you do not want any of the fuss, you can head over to HTC’s online web store for the US and get yourself a Developer Edition of the HTC One (M8) for a sum of $649 for the 32GB version.
However, (at least) one downside with the Developer Edition of any device is that it renders your DRM security keys invalid, as rightly stated by Android Police. It basically means that you will have to let go of any offers/deals that make use of the DRM keys, which might include (but not limited to) Google Drive storage, 3rd party content, etc. It is up to you to decide if this is worth giving up for an unlockable bootloader.