You might be right...
but at the same time I think you're not giving enough credit to the snapshot effect of the online calculators.
This snapshot is as capable of causing people to try to reduce their emissions by giving handy tips at the end which people might not have realised would make such a difference such as turning lights off in rooms when they leave them, turning off their PC's at the end of the day at work instead of just leaving them on and walking away.
The gadget mentioned in the article would only ever appeal to technophilic people with a hint of OCD about them who love nothing more than to look at stats all day.
You don't need a hand held device which consumes energy to tell you that you should walk the 1 mile from tube station to your office instead of getting a cab - that's just common sense - and indeed most energy saving methods are common sensical which the 'snapshot' diagnoses that the online calculators are able to nudge along perfectly well.
Think about how change needs to happen - by lots of people rethinking their energy consumptions - not by giving technophiles with money to burn another LCD screen to look at throughout the day telling them how good they are because they took a train instead of driving to work.