In both cases all you have is a soft bumper, I do not really see what may differ, mechanically. The only difference is the position of the bumper, at the top, or at the bottom.
While the O-ring can expand a lot while pressing down, a silicone ball within the small inner stem cannot. Because of this the resistance should increase quicker and thus reduce the mushyness of O-rings. At least that's what I think should happen, I haven't tried this mod myself.
^^This. The balls from IMSTO in particular are like this, the punched "hourglass" shaped pieces of rubber are perhaps the closest to orings, with the cut pieces of orings somewhere in between. I like all three, but they all feel different.
You can adjust the feeling of the mod based on both materials and shape, not to mention where the effect starts by adjusting the height of the pieces.
I highly recommend the silicone balls for the mod if you want a softer landing and to prevent the bottom out noise without the mushy compression of orings. It starts out softer than orings, but the resistance increases quickly due to the shape of the area under the stem for the ball to deform into.
Since the mod is in the switch itself you also don't need to transfer orings when changing caps or experiment with different oring thicknesses or numbers for different profile caps. SP DCS profile in particular can be problematic due to the lack of crossbars in the caps and different stem heights for each row.