Something else I'm curious about:
You say that you use this thing in the manner where you "hold the camera away from your eye".

On a non DSLR camera this won't cause any issue, but on a DSLR a potential issue could arise when Shutter Priority or Aperture Priority is used for the shooting mode.
(possibly Program Auto mode too, but I don't know as I never use that mode).

If the operators eye is not at the viewfinder whilst not in live view mode, the exposure will be affected, and the result could be inconsistent results from exposure to exposure.
Any light entering back through the viewfinder and into the optical system will affect exposure. A DSLR's metering system is embedded up in the prism housing.
Covering the viewfinder would be recommended if using this method to shoot.

Theoretically tho if live view is used on the DSLR, the metering will not be affected as the mirror is already raised and the sensor should be doing the metering.
(never tested for this myself, but I'm sure this is the case for exposure and metering tho).

Manual exposure should be used without the assistance of Auto ISO to eliminate the possibility that metering and hence exposure could be affected.

P&S and bridge cameras don't use relayed optics through to the viewfinder, so you won't see this issue.