well its not so much that is "bad" per say, but they are just ripping you off. I dont suggest buying any live sand ever. They all rip you off, and are most likely NOT what the company/lfs talks them up to be.
For example, arag alive, a lot more often than not, will have basically nothing live whatsoever about it. It may have a bit of bacteria, but there is a VERY good chance you're not gonna get any pods or anything (which is what you want out of live sand).
Think about this....how long has that bag of arag-alive been sitting at the store on a cold shelf? And add (or subtract i should say) the fact that theres basically no water in the bag to wash away any amonia that comes from dead stuff in the sand, and it will make even more stuff die in the bag because the already existing bacterial die off will cause higher spikes.
But the main reason for not getting arag alive is there is NO point imo....all sand turns live eventually anyways. Why not just get dry sand at half the price (or at least a lot lower price) and not have to deal w/the possible amonia and whatnot?
Now the "live sand" that the LFS might sell you is most likely stuff that they put in their system....for only 3 weeks, at which point you might not even get the bacteria (which is the quickest stuff to spread). And they charge even more for that than arag-alive in some places.
I dont know...i just see absolutely NO point in paying a load of money for something that is in no way what it is labeled/talked up to. Why not pay for cheaper dry sand and get a scoop of LS from a REAL established tank thats been running for a longer time?