Like others mentioned, the yellow backs are straight up rock salt. Rock salt is not as effective in extremely low temperatures, and hence not too good on concrete since it will get into any cracks or absorbed and then when it refreezes it can crack concrete even more. Ice melter is typically calcium chloride or potassium chloride, and the freezing point is lower so it can avoid refreezing a lot longer, so the water has more time to evaporate and not refreeze on the surface or in any cracks, making it worse.
I usually get some of both.
Rock salt, I usually get these from Rona
Marco Ice Salt - 20 kg @ $4.99)
Marco Ice Salt - 40 kg @ $8.69)
And for ICE melter I typically get what's on sale:
Alaskan Premium Ice Melter - 20kg - on sale now for $14.98
People can try to PM HD, but sometimes my HD will only PM (but not beat by 10%) if the item is on sale at competitor.
Scotts EZMelt - 20kg also on sale for $14.98 right now.
Sifto Safe Step Xtreme Ice Melter (20kg) some stores have it down to $5.98 (but not much stock left) - this one however is decent at melting, but I found you need a little more than others, since it is more in the form of "heavy flakes", instead of similar texture as rock salt.
All of the above were pretty good (for my use at least). All pretty effective.
This year (even though I had plenty from other years) I decided to buy a few of these since they were on clearance.
Marco Ice Melter - Yukon - 20 kg @ $5.50 on clearance.
This one was just "OK". I found it is does not act as quickly as the others, but it does the job. Then again, this year when I used it the temperatures were REALLY low (>23C) so that could have affected it's efficiency. Also found it was a little courser (bigger pieces) than all the others.
I am pretty liberal with the use of my salt and ice melters. I go through about 100kg a year (has been years I've gone through more than that). So far this year I have gone through nearly 40kg. Don't want anyone in the family slipping, and I have 1 tenant also, and don't need the hassle. I use the ice melters primarily on my concrete entrance balconies, stairs, and landing pad. And I use the straight up rock salt on my asphalt driveways and city sidewalks in front of my property.
Outside in the front of mine and my tenants doors, I have some large hole rubber mats (similar to these but larger holes), to help in avoiding to drag in any salt or gravel from the outside. They do help quite a bit, and very simple to lift and get rid of any accumulation as needed.