Live rock from established tank

[Pennywise the Clown]

I'm lucky to have an excellent LFS 20 minutes away from me, and a bonus is that they are a Red Sea stockist too.
My original plan was to use Marco rock (£5/kg) but visiting the shop today, I was told that they also sell quality live rock from their established tanks. At £15/kg it is a lot more expensive but shouldn't break the bank to fill my planned Red Sea 170.
If I went for the cured/cycled rock, would I have to add fish straight away to stop the bacteria dying off?
Are there any drawbacks to using this rock?

Thanks

 

[hijinks7]

I would wait a few days. You will have some die off going from the LFS to home unless you keep them under water. Most will transfer them with like a wet towel or newspaper

 

[ReefSlice]

Buy 90% Marco and a few lbs of live rock, this will seed your dry rock and your cycle will be sped up significantly. The bacteria will not die if not fed.