It would indeed have been cheaper, but on this occasion due to a perceived supply problem, all that appeared to be available was the Hornby chip installed X version of the 2Bil.
This chip clearly does not work very well on DC, unless you only ever want to run it in one direction. But even then, It also suffers a performance hit on DC - slow running characteristics were muchimproved once the chip was removed.
I am sure that the chip was not defective. As designed it appears to work on DC 50% of the time