Boy are you in luck. I actually have both of those exact same cables. I got impatient waiting for Atlanta Hobby's so I ordered the one from ReadyMadeRC. Turns out, they both showed up the same day.
ANYWAY...
The two differences are:
RMRC cable:
(1) Charges the GoPro battery. This means the GoPro will drain your LiPo and therefore your flight time. Not desirable since the GP3 battery should outlast a whole day's worth of recording multiple flights and multiple LiPo's.
(2) Exposed cable
AH cable:
(1) Does not charge the GoPro battery which means more flight time.
(2) Has a nice white sheath around the cabling, making it a little nicer to look at and a bit more protected than an exposed cable.
I hope this information serves you well.

ANYWAY...
The two differences are:
RMRC cable:
(1) Charges the GoPro battery. This means the GoPro will drain your LiPo and therefore your flight time. Not desirable since the GP3 battery should outlast a whole day's worth of recording multiple flights and multiple LiPo's.
(2) Exposed cable
AH cable:
(1) Does not charge the GoPro battery which means more flight time.
(2) Has a nice white sheath around the cabling, making it a little nicer to look at and a bit more protected than an exposed cable.
I hope this information serves you well.