In the changelog, it points out that upon installation of this particular update, the radio would be a whole lot more stable, with the camera also being more stable, while the other segments of the handset that will be more stable will include the FM radio and the Video Highlights feature. Apart from that, this stability update will also see changes (positive ones, hopefully, from the point of view of the end user) to the weather app that concerns the barometer.
The entire update weighs in at 66MB, where your firmware version on the HTC One (M8) will be bumped to 1.54.401.10 as well. It is recommended that one remains connected to a Wi-Fi connection during the downloading process, with at least 50% of battery life left. Do bear in mind that this particular update is being sent out on a staggered basis, so you will have to play the patience card if you have yet to see a notification on your HTC One (M8).