I’ve used this harness for years, and I have yet to come across something better in terms of security, simplicity and generally not being able to notice you’re wearing a harness.
I was eternally skeptical, however even the ol’ “boxer brief band with O-ring” is not as secure as this has proven to be for me.
Clear elastic is easily sourced, although I’ve made it with all different types of elastic and it’s still great.
What I especially love about this harness is that it allows one to use an STP easily due to the elastic having a lot of give to move things where you need them to be.
World’s Simplest Packy Harness