Survival is good and scales very well with your gear.
But it has high minimum requirements.

You need at least 700 agi to go surv spec.
If your crit is lower than 30% after getting surv talents, you are not "qualified" for going surv spec.
Keep in mind that surv spec has different shot rotation from BM hunters. (BM just need to spam steady shot macro due to their atk speed)
This shot rotation is extremely mana costly. (AS/MS cost a lot)
If you have low crit, you will end up getting oom faster instead of saving mana.

One more thing, as a hunter, u must use FEL MANA POTS instead of Super mana pots.
It is guaranteed 3200 mana. The fel ache effect doesnt affect us at all.
Engineer pot is just normal super mana pots in stacks. The 3000 proc is all luck.

1 thing sucks about surv spec. Your farming is gonna suck since your pet cant hold aggro at all when you are critting like so damn hard like mofo.