I made a copy of one (on each of the simple sling and the tactical sling as shown in the manual) out of top quality materials and it freakin rocks IMO. I could make them for like $30 or less, if there was enough demand. I have my prototype at my sewers getting the first one doen up for evaluation.
lots of guys like that ert sling tho too. they cost a lot more and are more complicated.