Nothing wrong with 2x 5s lipos in parallel to make 5300mah, and the 3s ones are fine, though the 30c packs are somewhat cheaper and more proven.
Not that charging connector though, you want
something that does the opposite (2x3s > 6s); unless you have a powerful charger (100-150watts) though it wont be quicker to charge two packs at once, you'd be better off charging them seperately or getting another charger; the
Thunder Ac6 is only $55 and is the same spec as the $130 Hyperion 606i...