Time for me to change my unit so have a new Daf ordered with small cenre axel, most of my work is paid by the tonne so thought it would be the way to go. Has anybody had any experience of them as you could put my knowledge about them on the back of a stamp 
No difference to a standard, you dont even notice it is there after a while
Salesman says it should be 600 kgs lighter than standard would that be reasonably accurate?
probably be able to save that with alloy rims fitted on the mid lift. It depends on whether you are going to make your money back with extra payload. We had them fitted on the tankers as the loads are paid per kilo.
we run dafs with standard wheels on midlift & a firm a friend drives for have the little wheels non steer midlift with alloys & his unit is half a ton lighter than mine with steel rims.
have one on my daf xf. unit and silo tank weighs in around 15,67. which i think is slightly lighter than the normal axle, we also have alloys fitted alround except on the mid lift.