I'm not sure where all the references to "chemicals" are coming from. I think there might be some misconceptions floating around.
Buffers and Baking Soda are essentially Sodium Carbonate or Sodium Bicarbonate. They are not chemicals.
Ask yourself what KH measures .... it measures Carbonate Hardness.
Crushed Coral is simply carbonate based, thus as it dissolves it increases the carbonate hardness. Baking soda .. crushed coral .. both carbonate based.
Whichever road you take to increase your KH, it all boils down to the level of carbonate in your water. Be it Baking Soda or be it Aragonite Sand or Limestone rock .... etc.
It can take a while for crushed coral to dissolve and get the desired affect. Even still, depending on your tank's volume a cup or two here may not be enough. Of course it depends how high you want to raise your KH. But certainly a 1/2 tbsp of crushed coral will do absolutely jack for your water. Personally, I think crushed coral does a better job of buffering when used as a substrate vice a cup or two here and there.
I honestly believe the test on a 5g bucket is worth the shot. You'll notice that w/ Baking Soda the results are immediate and contrary to what has been said, it does last a long time. I use it in all my AFrican tanks.
Now take another 5g bucket and put a cup of crushed coral in it.
You can then compare the results for yourself.
Don't get me wrong, there is no right or wrong here. Its just a matter of different methods .. so don't think I'm flaming those "crushed coral" fans
However, Baking Soda is super cheap and is not a chemical. I prefer it over crushed coral because it acts quicker. In the end, they both raise Carbonate Hardness (KH) .. I just tend to feel one does it faster than the other.
AS for Cichlid Buffers .... those are just well packaged containers of Baking Soda. If you are using things like "AFrican Cichlid Buffer" and want to save money then don't use it anymore. Instead go buy yourself a few containers of Baking Soda. I purchased 10 pounds of baking soda for about $4. I think a small container of Cichlid buffer costs about $6. Talk about Saving money