Those are certainly not new, my dad told me stories of testing this out in the early 50's. The method was introduced about the same time as the "telephone crank method" was popular.
Both methods were extremely productive, if used correctly. As it is today, with many new products that produce well, finding the right location to use, and more importantly, you must target the species that you are trying to "catch". "Shock", and "blast" as they were named shortly after introduction will catch multi species.
Several states have written laws to try and control their use, yes, they are that good, much like today's newest product, "Slab sauce". Fortunately for us crappie anglers, Slab sauce payed their dues upfront, and legislation is not expected. My guess is that lobbyists were used.
You are fortunate to find "blast", must have been discovered at the estate sale of a retired fishing guide.
Be sure to check your electronics carefully before using, a police scanner might even be helpful.