Mine was 2nd hand.
The electronics took a lot of fiddling about to set up and finally the oil seals let go. It sucked all the oil out the transfer box and spat it on the road. I spent a month touring down to Morocco and back emptying the oil out of the overdrive and putting it back in the transfer box! I grew to hate that overdrive with a passion. Then as a final straw. just north of Madrid on the way home it took to changing in and out of overdrive randomly even with the electric pact disabled, Luckily I had the transfer gear with me to put it back to standard. Took an hour and a half to get back on the road minus an overdrive, and Spain I'd like to say sorry for the oil slick I left but the oil was still bloody hot even after leaving it to cool for 1/2 hour and it made me jump about a bit as it ran down my arm.
The truck was faster and more economical with the overdrive in the back of the truck than on the back of the transfer box. 28% increase in gearing on a 1:144 transfer box with a stock tdi was too high.
So there you have it. I may have got a Friday afternoon overdrive but it just didn't work too well for me, my good lady wife absolutely hated the thing and she wasn't the one doing the oil swap job nightly in the Sahara