A Sony NEX-5 as a backup to a Leica M9? Yes, with an adapter for Leica M lenses.
It’s fun shooting the NEX-5 with its lovely LCD screen, but ergonomics are somewhat awkward. Using the magnification feature is very helpful, but also a bit tedious handheld, with no way to brace the camera as with an EVF which allows contact of the camera body with the face.
And with steadily advancing presbyopia, an LCD-only camera only gets more problematic as one’s eyes age. I found the total NEX-5 + Leica M experience quite fun at first, very engaging, but I’ve concluded that it’s fiddly enough to distract from image making. Others might have differing views and I certainly acknowledge that.
The Sony sensor is surprisingly noisy at ISO 200, rather disappointing after using the impressive sensor in the Fuji X100. I’ve sent the NEX-5 back— I’ll wait for something better to come along, perhaps the new Sony NEX-C3 or a new 4/3 format camera or the Ricoh GXR, all of which already take, or will take, Leica M lenses.