Radio-signal doesn’t go through metal, so sticking such a thing inside a metal bell blocks the signal, except where no metal is.
ie, if the top half of the bell is metal, and the lower is plastic, the signal can only get out through the lower-half.
Test the product, to discover how it actually performs, please.
There are many bogus products in our world.
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Pinion seems to be the ones who are getting it right, to me:
I’d look only at bikes based on their geartrain.
( I’m sticking with derailleurs, simply because that’s what I got, but … yeah, I can really see switching & ditching the grease on the pants bullshit )