Went for a two day hike and here is what I think.
The SO pocket is larger and holds more stuff, but I could not close the zipper with one hand, which is a real detriment and is real frustrating. I could only get it about 2/3 to 3/4 closed with a single hand. The zipper size is overkill, being way to large for a pocket. I have it attached at the two farthest opposite places so that it is not loose and yet still is not an easy close. Also noticed that my hands/arm would brush against it, though not much. Likely because of its thickness.
The Zimmerbuilt worked very well. Easy one handed operation. I was in and out of it all the time to pull the compact camera out. Also think it would handle rain better as it has sort of a top with the zipper being a bit lower down the side. No hand/arm swing brush noticed at all. Though smaller, I found it a better suited add on to the belt.
There you have it from my perspective.
Happy Trails.