Gravity?

What's up fellas I need some info from all of you that use house and garden. My question is can and should I still use gravity with the house and garden line. I'm running the whole line which I use to also with AN but the guy at the hydro store said I didn't need it. Any body use it with HNG?

http://datasheets.scbt.com/sc-236284.pdf

is it really worth the risk?

id say drop the gravity, ive mixed and matched using canna and had weird results, not saying that was it, but...