Delivery of new Trucks

I’m a newly qualified class 2 Driver. I’ve recently applied for a position delivering new lorries and returning old lorries, along with some cars and vans inbetween, I asked the guy I spoke to about using my tacho and he said I didn’t need to use my tacho as most wouldn’t be calibrated correctly just to keep a record of my driving. Are all driving hours still the same? Is this true, any help would be much appreciated.