What do you mean by “coveted Depth of Field” …. Shallow?
The results of using the EF adapter is the equivalent of having a 7.2 time multiplication factor with the EF lens you use.
In other words, if you were to use for example a Canon 35mm EF 24mm lens,
it would give you the equivalent look of a 172mm telephoto lens.
A rotating glass system like the P+S Technik mini35 allows you to take advantage of the true focal range of the lens attached. For example a Cooke S4 14mm prime lens will act as a 14mm with no multiplication factor, and give you the equivalent depth of field as it would on a 35mm camera.
The negative side of using the Mini35 is that the system causes a 2 f-stop loss of light, so you have to use very fast prime lenses in order to get a shallow depth of field.
With the redrock micro 35 you use your standard mounted lens, as well as the adapter, and the 35mm lens.
Also depending on the 35mm lens used some vignetting may occur.
I think the biggest factor is what kind of a budget do you have,
and what kind of quality would you be satisfied with.
Also what are your lighting capabilities, as that will factor into lens choice.
Some will just purchase a mico35 indie bundle for $850.00
and add a Nikon 35mm SLR lens for $800.00 and that will be fine for them.
Others because of cost, will rent the P+S mini35
and a set of super speed primes, as they don’t have the extra $15k setting around for a used lens set.
Still others, when they have a project that needs a high quality look
will step up from 1/3″ CCD cameras like the XL2, and rent a pro camera along the lines of an SDX900 with a nice HD zoom lens to give them the results they are after.
There are ways to achieve a shallow depth of field using your stock 20x Canon XL2 lens by adjusting your shooting style, and placing the camera, subject, and background at different depths.
Good Luck!