The secondary is most likely on axis, mounted in the same manner as the on-axis system. However the secondary assembly will be supported on a solid plate mounted in one corner of the telescope truss. The field stop, again at the prime focus, would be supported in a way similar to that described above. Primary always in partial, non-uniform illumination. Primary illumination is constant and uniform.
Primary illumination is unchanging with pointing orientation.
Well studied in other telescope designs. Unknown if support can achieve high figure requirement. The essence of this distinction is that the non-uniform illumination, both in time and across the mirror may induce undesirable figure changes. On the other hand the off-axis mirror is supported about the periphery of the substrate, which is not symmetric with the surface figure. In Spite of the apparent symmetry of the support the shape change will not be symmetric with the true figure.