Some users may balk at the lack of Bluetooth, but in essence this is the anti-Bluetooth dongle: the better bandwidth and greater range of Wi-Fi means it should be leaps and bounds better for sound quality and stability of connection.
While the app itself is a DLNA server, sadly, it is unable to access other DLNA servers on your network, which means for the time being you're stuck with the music stored on your phone: no streaming from a NAS or Windows Media Player.
While the app offers access to music-sharing site Soundcloud, I couldn't get the app to connect: it would let me enter my username and password, and then simply showed a whirling "wait" graphic ad infinitum.
While the player is designed to use at home, it can also be changed to permanent hotspot mode for traveling outside. All you'll need is your phone and an audio system to connect the Rocki to. Judging by their website, the makers seem to favor '80s boomboxes, but anything with a line-in will work.
The advantage of the Wi-Fi connectivity of the Rocki system, as opposed to Bluetooth, is that you can leave the room and not have the music cut out. Indeed, Rocki is designed to be a whole-house system and the company claims that there is no upper limit to the number of adapters you can use, so long as you and the dongles are within reach of Wi-Fi.
If you like to control the sound of your components, by using an external DAC for example, then the forthcoming Play+ might be of interest to you. It's a similarly shaped dongle that also includes optical and HDMI outputs. It will retail for $89 (roughly £50 or AU$95, converted) which is still hundreds of dollars less than similar components like the Sonos: Connect and Samsung Link Mate, and also manages to one-up the $149 analog-only Phorus Receiver.
To get going, you simply click on the Start button on the front page of the app, and Rocki pretty much does everything else for you. The unit creates its own ad-hoc network that the app searches for, and once detecting it, the app asks you to input your home network password. Unlike most other Wi-Fi device setups, you don't even need to touch the new unit, just plug it into the power.
By comparison, the setup of the more expensive Phorus system was heart- (and router) breaking. The couple of minutes I spent setting up the Rocki were a joy compared to having spent at least an hour tortuously troubleshooting the Phorus, which had permanently disabled the wireless function of my router.
For such an inexpensive unit, the Rocki really performed beyond expectations. Yes, the build quality is a little iffy, but it seems that all of the money has been poured into its performance instead. No, you won't quite get the hi-fi performance you might expect from a dedicated system like the former Squeezebox Touch, but at as much as one-sixth of the price of most competitors, it doesn't matter.
For example, in practice there was less difference than I had expected between the Rocki and the USB DAC on the TEAC A-H01. With Arcade Fire's "Reflecktor" the differences were very subtle, with a tiny bit more air on the TEAC. Both sources were able to convey the deep bassline and sometimes overwhelming amount of instruments in the soundstage equally well, though. With a more "rock" track like Future of the Left's crunchy "Small Bones Small Bodies," there was better vocal detail on the TEAC, and the guitar and bass were easier to tell apart from each other. But given the price differential -- $49/£40 versus $299/£239 -- this wasn't bad at all.
Playback control can be spotty: I found sometimes it's not possible to stop a playing track, while the app can also start playing the song from your last session, even with an empty playlist. Similarly, depending on the strength of your network, you may find that you get the occasional dropout, but if you have a dual-mode (2.4GHz and 5GHz) router and a compatible phone, this should fix any small issues
Finally, when using the battery, I found I got a couple of hours playing FLAC files out of the device before the app crashed, and I was only able to get the system working again by plugging the Rocki back into the power socket.
If it offered support for more music sources, the $49 Rocki Play might be the kind of no-brainer for audio that the $35/£30/AU$49 Chromecast was for video. It's dead simple, plus you don't need to worry about wireless hubs, expensive speakers, or other gumpf. Sure, it's limited to playback from a phone at present, but this will likely suit a large majority of users who just want to hear their portable music collection. But the potential of this ecosystem? I'm quite excited about where it can go.