There are a few ways to get root access on HTC's new lineup of smartphones, but root only gets you so far. If you really want to hack around, you'll want an unlocked bootloader and s-off. That's what you get with the new SunShine tool from Justin Case, Beaups, and associates. This time, however, the free lunch is over.
To use SunShine, you need to be on a device with a stock Sense-based ROM that has been rooted using Towelroot, Weaksauce, or something else. It has been tested on the M8, HTC One Remix, and a few other phones – basically anything HTC has made in the last year or so. You can run SunShine and it will tell you up front if it can unlock your device. Once you get s-off, you can access any part of the internal memory and flash all sorts of dangerous things, even swap out the entire ROM, recovery, and bootloader for something else.
Now for the unusual part – this tool costs $25 per device. You make the payment in the app via PayPal or credit card. Each phone is licensed based on a unique ID so the tool can be used more than once if you go back to s-on for any reason (only on that one device). As for the cost, the SunShine website explains that tools of this nature are not easy to develop anymore. The team has racked up hundreds of hours and killed uncountable devices to make this happen. If the alternative is buying a $700 developer device vs. a $200 on-contract M8, $25 is kind of a steal. I don't see any problem with this personally, but you know how the internet can be.