So, I got my OpTech strap after only a few days. Installation was rather easy although a bit fiddly, because the eyelet on the camera was on the slim side. For a right-handed person you must install the strap on the left side of the camera, otherwise it'll be in the way, i.e. in front of your face.
I'm using the strap with my Sony Alpha A580, I will get the original battery grip tomorrow, so I will fasten the second connector on that one.
Here's an image (taken with an Acer A700 tablet) of the installed strap:http://sdrv.ms/16lO2Wk
Edit 11.05.2013: Got my battery grip today and installed the second connector to it. Works like a charm.