This is a great idea, I've made some cords with the above linked plug. Never seen them with a locking feature, tho.
I do think you'd much rather use SJ cord vs. SO.
Paul, there isn't a day I don't learn something from this forum. For 30 years I have called any rubber jacket flexible cable SO cable. Had a guy I used to work with call it locomotive wire. The key being the find strands in the conductors that make it lay nice.
Well anyway it turns out I have SO and SJ and some stuff from Emerson I can't cross reference.
So many forums don't want to offend people and point out mistakes. That is for people who want affirmation not learning.
Keep on calling me out.