It appears it does not what??? have MUTE Key? Cord Cutters had review of it, shown the remote up close and shown it has mute key!!
Again, I was working from the wikidevi information on the device. Since they are usually working from FCC filings, it might be possible the the images sent to the FCC are from the top instead of showing the side with the mute or they just missed it.
That review is extreme helpful. I wish I could link to it. Maybe a community manager could bypass the vagueness of the Roku Community "guidelines" and provide the link. It provides a more well rounded answer to the OP's question.
The review also brings up the new remote buttons are physically quieter that the previous one. Since the Roku defaults to "menu volume" being on high, I don't know if most people would notice the different to how the physical button sound. The menu volume causes the TV to also produce a click which may mask the physical sound. But for people that like the menu volume to be set to off, reducing the sound from the remote itself might be a welcome improvement.
Also he brings up that the remote removes the A/B gaming buttons. Anyone that bought a game that requires those button may want to put off upgrading. Overall, I have been disappointed in how Roku has handled gaming. They had a different development API for major game developers to allow for better performing games. Android has a similar concept called NDK. But unlike with Android, the information on Roku native development environment was restricted to a select few developers instead of released publicly. With the growing popularity of the webassembly standard in browsers, I was hoping we would someday see similar performance changes to the Roku interpreter. Instead it seems like Roku is moving away from promoting gaming as a function of newer Roki.
The review also shows the power supply as being yet another wall wart that requires extra space when plugged into a power strip. There are some power strips that take this into account in how they space things. However, I really wish Roku would provide an in-line power supply. It is common place to use wall warts for media players so this really doesn't impact how well Roku competes with other products. But I do appreciate the companies that move the power supply behind a cord that allows the power plug to have a narrow width.
Lastly, the review better answers the channel load and video start-up performance. It is what I expected that it varies between channels and is only a slight improvement. He seems to echo my statement that it is a nice to have improvement but not enough that existing Roku Ultra owners should be concern with rushing to upgrade.
All new roku remotes are quiet at first, after some use they start to make sounds when touched. Check out walmart, best buy, or amazon for just released rc-al7r, its wifi remote sold separately that works on express up to roku TV's, it has mute key. Its $19.99, no headphone jack though.