So I have been making a simple cuff out of straps that is more comfortable than the previous DIY project, and finally came up with this. First of all, I must state that it is not an easy snap or clip on kind of restraints, and it does take two hands to remove it, thus, it is good (at least in my eyes).
Below is the simple three step process. And I hope more can benefit from this exploration instead of spending $$$ on those expensive import. Humph!
I have upgraded the choice of material from those kind of seat belts to this, more of canvas quality. The required length is 85cm maximum, and it is a 1 inch width. Burn the ends with a lighter to prevent and fluff from coming apart.
Run a strap adjuster to each ends and bring it to somewhere close to the centre.
Lastly, run the ends of the strap through the fastener and it will create a nice tight loop.
Please note that this cannot be undone with just one hand, so feel free to tie both hands close to each other. Give it a few trial and error, to see how loose or tight it must be to prevent the sub from escaping. Safety first.