I built 5S and 6S pacs from a123s taken from Dewalt 36v power pacs. I would advise wiring them for balancing. Its pretty easy and the harness/tap I used was $2.25. It took me all of 30min to build a 5S pack including the balance wiring. These are supposed to last 1000+ or so cycles and in the interest of that longevity, I wanted to balance them.

I use a Hyperion 0610i balancing charger and there is always balancing activity when I charge my a123 pacs. I run a pr of 5S pacs in parallel so it is effectively a 5S2P pack - need that for run time, 2300mach is not a lot of capacity. These cells are indutrial in nature and were adapted to rc when plane guys figured out they were 30C capable, so I don't think they are as carefully produced as a rc intended lipo batt. There is prob more variation in manufacturing these than with something like a lipo cell at the Kokam plant.

You can charge a123s without balancing - you can prob get a few dozen charges before there will be enough imbalance to cause probs - but depends on how you're using them too - if you're pulling them hard, will see more imbalance versus easy duty. These cells can vent when they have major probs - have seen the pics and some just go bad - they quit holding voltage.

With my 0610i charger, its just too easy not to balance everytime. You can charge these at low rate and they'll stay closer to balanced. Guess a low charge rate gives cells enough time to lessen the impact of cell to cell differences.