I do not need any more bags but i am very interested in this thing. The few times i have carried both front and back with my 5.11 gear, i have found that it REALLY DOES alleviate the feeling of weight when balanced out correctly...but it also does look ridiculous ...especially in an airport environment. I some times see people doing it but they are usually ones looking like they are heading for an outdoors adventure. It gets even weirder when a dude in a suit with a beard, sunglasses wearing a Gatsby cap comes walking through with front and back duffel carry (which would totally be me)....
What i like about this bag/sytem though is the security features and the understated almost quasi pro look...the fact that it comes with a small packable bag (which could be your boarding bag) is fantastic for the money. Both bags come with water bottle and lap top holders and the fact that the 40L has the hard shell protection case at the top for your head phones and glasses etc seems pretty sweet.
This also seems like it would be a second only to the Peak travel bag for general sight seers and tourists looking to keep their hands free while on the move.
It is intermittently on sale at Ebags for as low as $139 US (normally $199) which is pretty sweet.