I am guessing that BadPapi is actually commenting about using CA from a pool store instead of the actual listed ingredients themselves. Presumably, this goes to the general trust that the listed ingredients are what is actually in the product. Mind you, the bad stuff will be in the fraction of a percent listing. His point obviously has merit. Notwithstanding, I did not view any of the listed ingredients as harmful. When you mix the 2 part, be mindful that this is 83-87%, as some recipes use the high concentrations.
Notwithstanding, I personally have used CA from a pool store for many years with no issue. The stuff I had was in small chips and not powder, which made it easy to dispense (no dust no clump). So the answer is - in theory, YES, but you have to trust them. I don't view this as too dissimilar than to trusting other bags of CA or magnesium sulfide that is billed as ice melt at Home Depot.
When I was in Miami, it was even more readily available than it is in MA, and there is no ice melt in Florida. As for cost, it is far cheaper than buying CA products from the LFS. But it is no more expensive than buying in bulk from Bulk Reef Supply - a source that is specifically for reefers and I trust. Many LFS also carry BRS products (I bought some from Jays before).
http://www.bulkreefsupply.com/brs-bulk-calcium-chloride-aquarium-supplement.html
So my thought would be to use of what you have, if you bought it already. And for the next purchase, buy it in bulk. If you have a spa and can otherwise use it, then just buy in bulk now as it won't go to waste.