I forgot abt the erection part. Yah it will be very painful if erect in the tube clamp damn. Adult everyday will see hot sexy amoi, sure erect one lulz! Before go clinic wanna remove the clamp need to soak in water at home to loosen up the clamp so that easier to take out. But in rare case, clamp difficult to take out do happen. So gonna have pain 2nd time like u said.
No need say clamp, even circumsized handfree traditional way, if suddenly erection also very painful already coz it pull the stitched skin that not yet used to be stretched.
Children do erect especially the time wanna go pee, and during sleep at night. It simply erect itself at night.

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Erection will be painful, whichever method you choose.
It will be worst if using clamp method.

At least if with stitches or stapler, the wound won't rip open so easily.

Yes coz the clamp size is fixed and small. Cant imagine the pain if erect in it damn.