no difference really in terms of quality. the heather grey ones were definitely a lot more limited thant the cool grey pair (although youre wrong about them being instock on FNL theres only a size 9 left). I'd say the limited factor and the fact that they were the first of its kind is what makes them more expensive. But what gives the black toe pair a HUGE advantage over the heather grey pair is that since the toe cap is clear and not breathable the toe soaks up sweat and changes color on you. Doesnt happen wityh the new ones because of the darker color and the black toe cap. so if you plan on wearing them regularly i wouldnt bother with the heather grey pair.