LiPos for my dual BL?

[JOHNNYMAXXIMA]

Well I'm still wanting to go LiPo so I called FMA the other day. I talked to some guy over there and he pretty much said the same thing that MetalMan and Mike had said. I need to get 4 2s packs. The only other thing that he said that kinda confused me (very easy to do) was for me to use this.
I'm not sure if I need that or not, what do you guys think? I read the description on it and still cant quite figure why I would need it.
Thanks.