I have very sensitive hearing, and trouble understanding speech. I
depend on closed captioning but it often blocks the screen.

I heard about a product that raises the volume when people whisper and
lowers it when they shout.

I think there are three different ones on the market: "TV Sound
Regulator", another "Audio Leveler", "Volume Stabilizer"

"automatically corrects broadcast volume by adjusting it to a preset
level selected by the you."

I heard that magnavox has a similar technology, but I have a JVC.

Does anyone know if this is a gimmick or if it really works? Which
ones work?

Thank you, from someone with sever hyperacusis.