Richard - I'd be interested to know (generally - I don't have a 2.5 and will not) whether the AFR measurement is bridgeable.
My understanding is that for Euro5 it has to be "tamperproof" and I know the Bosch ECU solution makes AFR dongles (sor far) imposible without ECU alarms. Because the AFR signal driver from the ECU out is NOT constant - and is timed.
Rule of Thumb - How "Not Cheap"? - G'wan tell us!.