Note: this was originally written in the end of 2014. I have since then sold the camera.
This camera was released in the spring of 2014. I picked one up for several reasons – I needed a small and pocketable camera that could deliver photos with a quality that made them usable for work (Newspaper print & web) in a pinch. At the time when it was announced I was also planning to start a small video project. The high video quality of the mk3 that DPreview called "a game-changer" even when compared to full-frame cameras, was also a strong selling point. On top of that the bright lens and the pop-up EVF was also two factors that made me buy it, despite the somewhat hefty price tag.
The RX100 mk3 has more or less constantly been in my bag since then, and every time I've looked at the photos I've shot with it I've been really impressed by the image quality it delivers. Even though it's 1" sensor is way smaller than the full frame one in my Nikon D800, there have been countless times when I've mistaken photos shot by the Sony for Nikon ones. I've also used photos shot by the RX100 for work, and my editors have never complained (I still bring my Nikon on assignment – of course – but there have been times when I've stumbled across something newsworthy when I didn't plan to. In those situations the RX100 didn't let me down).
The Sony is also virtually silent, small enough to not attract unnecessary attention as well as having quick and reliable auto-focus – factors that make it very suitable for street photography.
Even though I won't be selling my full frame Nikon anytime soon, I highly recommend the Sony RX100 to anyone looking for a small and pocketable camera. The mk4 has superior video features, so if you plan to shoot a lot of moving images it's worth paying for it. If you only do stills however, the mk3 will most likely suffice. The only things you'll be missing out on would be a better EVF, faster autofocus and a higher burst rate (16 vs 10 fps). The differences in (still) image quality are negligible.
So is the RX100 mk3/mk4 a street shooters camera? Sure.
It's fast enough, image quality is great and the small size makes discreet and unobtrusive (in case this is important for you, personally, I often shoot street photography with my Nikon D800, and I rarely feel that the size is a problem).
The only real downside that I can think of with this camera is a purely emotional one – I don't actually enjoy shooting with it. Even though the camera is solidly built, there's just something with the way the buttons and controls feels that makes me feel really disconnected from what the camera does. It just never "feels good" to shoot with this camera. Of course, the small size means that compromises had to be made in regard to handling. Sony clearly prioritized small size here, and from a pragmatic point of view, I think most of their design choices make sense, even though I wish at least they could have given the shutter button a tad more travel.
Of course, this is highly subjective, but for me, the reason I haven't used it as much as I had hoped is to a large extent related to this. One upside to the disconnected feeling while using the camera however, is that I always end up being pleasantly surprised once I've copied the photos to my computer.
So in short – If the end result is what matters to you the most, there's no reason to avoid the Sony RX100 for aspiring (or experienced) street shooters. But, if you prefer a camera that is also enjoyable to use, I would rather recommend either the Fuji X100 series or the Ricoh GR, both are terrific cameras, image quality is one notch higher thanks to their bigger sensors, and they are both very suitable for street photography.