They are likely quite true and effective for shield purposes, but out of range for myself.
Commercial sources are available but rather outrageous in their prices.
I really doubt that I'll ever find a adequate sized container, ready made via any source, so the choice is really not available, outside of this approach. Regardless though, it will be interesting to try it out and see how effective it really is over time. Other brands exist of course, but aren't known as to their aspects. The usual color of the AE torroid cores are bright orange, but black has been noted in other brands.