That's the one I had and used for a while, but it came apart on me...which is why I need a new one lol.
I use this one, holds together very well. http://www.autopia-carcare.com/rotary-3inch-backing-plate.html#.U1kosOZdW3Q
Yea, you really need the flexibly when using the 3. Simply because the only time your actually using a 3, about 98% of the time its always in a tight, contoured or both type of spot.
They're not expensive...it's the shipping that gets you. I don't need enough stuff to qualify for free shipping...just need this one thing lol.