The speakers for the Sprint versions evidently are different from the rest of the One M8 series, although Sprint hasn’t been bragging about this very much according to BGR. Those wishing to apply the RUU might want to wait a bit to see how it works for others, as the thing was just released about 15 minutes ago on xda-developers.
Much like the the fumbled Android 4.3 update for the HTC EVO 4G LTE, this update is coming as an RUU at the moment and will wipe your phone if you install it. It also makes your phone consider itself a test device, which means you’ll be telling HTC any issues that arise with your experience. That means your data is most likely theirs.
A stock rooted version that will not wipe your phone is claimed to be coming soon by benny3, so my advice would be to wait until that comes out unless you really want to run this RUU. If you do want to use it, make sure to have your CID set to 11111111, or whatever the post requests. There are no mentions of whether you have to do this if you’re S-OFF or if it matters one way or the other, but then again it appears it’s been out a very short amount of time.
I’m not currently familiar with whether you have to be rooted in order to superCID on the One M8 series, or whether the Harman/Kardon edition is even worth flashing. I’m assuming it is and the Sprint crowd have been waiting on some licensing or promotional issue in order for it to come out.
If you run it, drop us a line and let us know how it works for you. As of this writing, there were only two reported downloads on AndroidFileHost so … it’s really early on in this release. I’m probably going to sit on the sidelines until a non-RUU version comes out, or I get a report back saying it’s the greatest sound in history.