Actually no, I've read about them and have been meaning to try one but it's the one thing I always forget to "add to cart" when I'm ordering shave gear.
It's a good tool to measure your technique. They sting like the dickens when going over a nick or razor burn. Fairly cheap and last a long time if you don't drop it. They shatter in jibbles and bits. Best clue to keeping one in hand and easily gripped - wrap a rubber band around the thin side outer edge. That keeps the big flat sides open for use. They also can be used on finger tips to aid in skin stretching through a lathered face. That helps to flatten the skin and keep it taunt like a drum for less irritation.
I shave daily mostly and when I first started DE shaving a BBs was a goal and received a few. It really is not worth the effort to reach the pinnacle of a excellent shave. I'm happy when I reach my sweet spot CCS,DFS,BBS and to get a true BBS you will more than likely will remove a layer of skin & the objective is to remove stubble not skin. <24 hr growth <48 hrs growth <DFS,BBS shave <2 hrs later the beard is starting to come back! I took these pictures around 400 X magnification about a year back and maybe this is a good thread to show them again. Have some great shaves!
It lasts a good 2-3 hours! Long enough for me to enjoy my shave and my wife'smile at breakfast. As I said. To each their own.