For my choice I put the priority on internal view recording over external view, as I'm concerned about recording what happens in side for my safety/backing up what happens inside the car.
Features I would look for :
. Internal view camera (Necessity),
. Night recording must be via IR light not visible lights
. External Front view recording (Would be nice to help if in an accident, but not a necessity)
. Not bothered about HD quality as long as image quality is good.
. Instant recording on power up
. Can be powered via wiring into a switched live feed, already to many things having to connect via cigarette point.
. Built in monitor, that way passengers know that there is definitely a camera in the car. If not must have video out capability so can connect to a small screen.
. Small size
. Date/Time & GPS data recording
From having a look around, the best overall I can see would be one of the Roadhawks
The DC-1 seems a nice unit but is only a single camera (external view). Would be nice if they did that in an internal view version.
RH-2 or the RH-2 Pro are dual cameras (internal and external) and the internal is IR lights for night recording. I also like the idea with the Pro version where you have an external box where you can plug in a USB pen to record to. That way if someone was to attack/rob you, them nicking the camera would still leave you with the video. The Pro can also be connected up to a display for playback/live display of the video.
Youtube video of a night time recording on a RH-2 :
http://www.youtube.com/watch?v=qRrJsTErbyAThe only problem being the cost of them.
Just found a youtube video of the BlackVue DR400G (that the OP sells) facing inwards at night. Good quality, but don't think it would show much of rear seat passengers if little street lighting around as it dowsn't appear to provide its own lighting (visible or IR).
http://www.youtube.com/watch?v=wCZs8TRIMEY