Yes there are distinct advantages to Chromed Bronze bodies to the rigging screws.
One of the problems with s/s rigging screws (where the whole assembly is made of s/s) is that when the threads are under high pressure there is a danger of them 'galling' as you try and adjust them. This is where the s/s dry welds itself to itself and makes the rigging screw impossible to adjust any more. You can eliminate this happening by using bronze bodies in the rigging screws.
IMHO you are being offered the 'proper job' as they say down here in Devon.