Great links Lampwick.
I have been alternating between a beaded cock ring from adamandeve.com ($9.95) and a simple 1/2” elastic band (bag full for $1) doubled over and stretched around my whole package. The beaded ring is more comfortable and can be left on for more than an hour or two because it allows some circulation. The band is more effective and generates more engorgement, but should not be left on for more than 30 minutes, at which time your unit begins to become uncomfortable.
Caution.These methods should not be used on an unconditioned unit because they could cause problems such as extended numbness and blisters. I have ED and have been using these constriction methods for more than 10 years.
I would like to experiment with long term constriction to see if I can increase my girth. So far, I have only used a cock ring/band to enhance my unit for sex, but would like to use them to gain girth as well.