Fuel Consumption Monitoring

For those of us who have got electronic fuel injection systems, but hav’nt got the dashboard read outs, VDO have brought out a plug in data compiler that plugs into the truck electronics and displays MPG/ average or current on a display, see here
www2.vdo.com/vdo/business_custom … =1134.aspx
Commercial Motor tested one this week and seemed to be impressed by it, but at £600 notes would it be worth it?