I have. I have one on my Laney Ironheart. It’s a simpler form of the Blackstar ISF control. This is more of a tone ‘tilt’ control, so central is neutral, to the right is more treble and less bass, to the left is more bass and less treble. It's gentler and less peaky than the normal 3-band tone controls. You can treat it in two ways. One is to use it in conjunction with the EQ to help get just the sound you want, or if you gig a lot in different venues, you can leave your basic EQ settings as you prefer, and you use this control to adjust for the sound of the room e.g. if it’s bright sounding with lots of hard surfaces then turn it to the left, and for a dull room with lots of soft surfaces and drapes/curtains/carpets, turn it to the right.
Or whatever. It’s just another control to help get the sound you want.