SE Electronics guitaRF

Sturdy, portable and works well as a shield. The mic can only be mounted from the top, so if you're using a radial-address mic, it will need to be mountable upside-down (in other words, make sure it won't fall out of its shock mount if you do this). The hole can be used to hold an axial-address mic, which it does very nicely, with no need for any other stand or clip to hold it in place.

Very useful on stage to use Ribbon and dynamic microphones in phase in a single microphone stand.
Helps in the acoustic isolation of other noise instruments on stage.

Very useful things especially in combination with SE Electronics RNR1. I use it for each recording with guitar amplifier.

These reflection filters are pretty cool and do a good job of isolating a guitar mic on stage. But they are super fragile, it doesn't take much to break them, so maybe not great for a lively band that like to throw themselves around the stage.