I use these on a upholstered `67 Deluxe Reverb.
Pros: If you?re careful & measure and mark before mounting, they?re easy to mount.
When tilting the amp you can get rid of a lot of phase problems that might occur when the guitar has it?s own microphone and simultaneously leaks into the vocal mic.
I.e. you can turn the volume up a little more, which is a benefit for most guitarists.
Cons: None really, they do off course add a little weight to the amp.