This is very similar to the blister I gave myself with a vac-extender. It was a little larger and lower (more on the underside of the glans).
Let me tell you, the exposed skin beneath the blister hurt like hell anytime something brushed against it. I had to bandage it for several days. It took a about a week to heal, but blistered right back up even under very low tension/vacuum. Give yourself a couple weeks (and maybe more) before doing any vacuum-related activities.
7 3/4" (+3/4") BPEL x 6 1/4" (+5/16") EG