Usefulness of 12-bore Chain Shot and Incendiary in WWI

I read about the 12-bore Chain Shot and Buckingham Incendiary rounds fired from shotguns during WWI. I wonder how effective these were. Modern rounds similar to Chain Shot (“Bolo Rounds”) are notoriously unreliable and ineffective. What was the conclusion regarding the Chain Shot shells?
Regarding the Buckingham, how heavy were the slugs and what was the muzzle velocity of these? Were they considered a success?
How many of these types were produced, roughly? Would they be difficult to find post-WWI, were they all destroyed or used up?