Feb-11 2018 Product Update
Update... The Purggo customer service team got in touch me.  Apparently I got an old version of Holdie Eyeglass Retainers.  Their new and improved version of the product works like a charm.  I no longer experience the slippage and the holders stay put as expected.  These straps always looked good.  They now function just as well as they look.
Rating: 5 stars