A strain relief is a bit of (usually) molded rubber around the end of a cable that prevents it from twisting at unnatural angles. Crappy pic:
A cable cinch is a little slider above the y-split of a cord present on most earphones. Another crappy pic:
Memory character is the property of a cable to maintain the shape it was placed in. The shape of a cord with no memory character is very easy to change. With the ViSang earphones if you loop the cord and put it in a case, it will still be looped when you take it out and may take some time to straighten out.
The plug on the Mp4nation models is indeed a little better but at the cost of strain reliefs that have been reported to come loose (on the M2) or no strain relief at all (on the M1). As for the FA Genesis, noone knows much about it. It's a newly-announced successor to the well-known Eterna and there's a pic of it on Fischer Audio's site and that's about it.