The center links of the bits are put on differently. The roller bit has the fixed ring making up the joint perpendicular to the D and the ring bit has the fixed ring parallel to the D.
Will your horse care? That depends on your horse. But as the owner of the pickiest horse on earth about bits, he would DEFINITELY notice that difference between them.
What position is the fixed ring on the bit you are currently using?
There is no joy equal to that found on the back of a horse.