I feel bad for the people who had negative reviews.
I ordered two items from this site and my TWO 3/8" Hex hole-saw extensions came quickly. Not to mention, they had best prices.
I would recommend, based upon my experience
Products used: Milwaukee 48-28-2010 6" QUIK-LOK 3/8" Hex
and also
Milwaukee 48-28-2020 12" QUIK-LOK 3/8" Hex