> So they don’t effectively block communication to and from the device?

That is impossible to know without knowing the characteristics of the signal, noise, attenuation performance, sensitivity of the receiver, and other environmental conditions.

> Or they don’t block all RF?

They definitely don’t.

If you want to attenuate an RF signal, you need to do RF engineering. There are products to help people do this (eg RF test enclosure), but they aren’t marketed as “blocking RF” because that is nonsensical. The products that advertise as “blocking RF” without any real specifications are unsuitable for serious RF engineering, they are primarily sold to conspiracy theorists, hypochondriacs, etc.