Anyone have any input on these systems?

I know a few people on the boards have them on their rides.
I know both plug into the OBD2 port.
But do they require to be plugged into the Cigarette Lighter as well?

For those that have the BLITZ R-VIT:
Does that speed only come in km/h or is MPH also available?

Also, please list Pros and Cons for the systems.
Any useful information would be greatly appreciated.

THANK YOU!
DRU