When I was experimenting with vacuum stretcher I found it extremely comfortable compared to anything else I’ve tried. I could easily have exceeded 6lb, and didn’t lose blood flow either (presumably the blood inflow is equal to the outflow, whereas a vacuum pump is sealing off the penis at the base due to the pressure of the tube on the pubic mound). I never suffered any blisters, and the glans seems remarkably resilient to lymph issues relative to shaft skin. That and also possibly because the vacuum device was molded on the inside to the same shape as my own glans, so there was no real air gap to expand into.
It’s single major flaw was that because it was soft (made from silicone), any disturbance or even minor misfit would introduce an air leak that would break the vacuum.
I might give the above design a try to see how it feels. My feeling is that the above design with a silicone glans molding inside it would be the way to go.
In the above picture is that 6lb really hanging only from the surface of a condom? or is it a catheter?