I have zero affiliation with the gentleman in the link and have never had any interaction with him in any way. I'm sure he produces a great product.
But......
This is what I learned when I began tying my own door straps. The picture of the door strap when you open his page, the first one, that's tied with 4 pieces of paracord.
The loops of the Paracord that go through the footman Loop in the door and the catch on the tub, I never discovered a good enough way to attach the Loose Ends of those pieces of paracord to each other. I tried melting them to each other but it wasn't enough. They almost need something like a butt splice between them to make them one solid piece.
Anyway, because I was unsuccessful at attaching those loose ends to each other, permanently, I tied the Cobra knots is tightly as I possibly could over those two loops because that friction is the only thing that keeps those two Loops from stretching and eventually coming apart.
The only way that I discovered to create a paracord door strap that wouldn't stretch or come apart is to use one single piece of paracord without any breaks in it, vs the 4 pieces used in those.
That said, someone may buy one of those door straps, take it apart and discover that he has come up with the way to permanently attach the loose ends of the loops to each other. If he hasn't, then over time with the door swinging open and bouncing off the paracord, they will stretch and come apart