Compared to Fujifilm FinePix X100

The RX1 is smaller than the Fujifilm X100 (the more recent X100S is identical in terms of body size and very similar in terms of control layout). The RX1 doesn't have the X100/S's hybrid opto/electronic viewfinder but, considering its sensor is 2.4 times larger, it's an impressive piece of engineering to keep the camera so small.
The body of the RX1 is clearly smaller but the lens (which is actually 35mm, rather than being equivalent to 35mm) is longer. Neither of these cameras is pocketable, but equally, neither is anywhere near as large or obvious as a DSLR.
Despite its smaller size, the RX1 finds room for a larger screen than the X100/S and makes good use of the few controls it does have - with three positions on the four-way controller being user-definable.

Compared to the Sony NEX-6

Despite only being slightly larger than the RX1, with its much more substantial grip and more protruding body elements the NEX-6 follows a different design philosophy than the RX1.
On the rear the NEX-6's electronic viewfinder and the different aspect ratios of the screens are the most obvious differences between the two cameras. The button and control layout however shows some similarities.
From this top view we can see the NEX-6's protruding EVF and grip versus the RX1's much simpler lines. The NEX is a little wider but with the 16-50mm powerzoom lens attached it's comparable in size to the RX1.

Accessories

A range of accessories is available for the RX1. This includes the optical viewfinder FDA-V1K, electronic viewfinder FDA-EV1MK, lens hood LHP-1, and thumb grip TGA-1. The viewfinders and the thumb grip slot into the camera's hotshoe and the latter has a hinge, so you can flip it back and still press the play button which is hidden underneath it.

The thumb-grip connect to the camera's hotshoe and it hinged to give access to the play button. The thumb-grip also comes with an integrated shoe, so you can combine it with the optical viewfinder if you wish.

At around $249 the thumb grip isn't cheap and, although we found it improves the camera's handling, the small plastic catch that holds it in place doesn't seem terribly durable (in fact on the sample we've been using this catch broke off).

At $599 for the optical viewfinder, $179 for the lens hood the thumb grip the mark-up on these items appears to be rather excessive but it remains to be seen whether future RX1 users will prefer the original parts, or steer toward the cheaper far-eastern knock-offs that will no doubt appear on certain online marketplaces, if they haven't already. The electronic viewfinder will cost $449.99 - $100 more than the equivalent unit for the NEX series of cameras.

The FDA-EV1MK electronic finder uses the same excellent 2.4m dot OLED display as Sony's high-end SLT models. However, the huge rubber eye-cup makes it difficult to get your eye near the screen - all the more so if you wear glasses.

The FDA-V1K optical viewfinder will, no doubt, appeal to some retro-fetishists, but the FDA-EV1MK is the more practical option, since it's cheaper and shows the camera's settings. Furthermore, it allows you to make proper use of the Quick Navi menu (since you can set the viewfinder and rear display to offer different display modes). Sadly the cost and an enormous eye-cup which makes it difficult for wearers of glasses to use, rather takes the edge of its appeal for us.