ECU Replacement New or Used?

[Shaff_Cake]

Hi All, been told that the main ECU on my W209 CLK350 is fried and beyond repair (it's been to Bosch and back). Quote for new unit from MB is £1500 +VAT; specialist I'm using is reluctant to work with a second hand unit (assuming I can source one) because he thinks the saving will be offset by the time he needs to spend 'reprogramming', I'm inclined to agree with him as second hand units seem to be sold as kits (with keys, ignition barrel and steering lock) indicating that they do require a lot more work compared to a custom ordered ECU...am I being misled??

Would really appreciate your views