The Yany Boo-Star is essentially a specially designed heavyweight modular neck screw with two optional weight attachments. It's designed and produced by Yanagisawa in Japan. There are 3 models available in this Yanagisawa/Selmer fit variant:

• Raw Alloy: Tonal focus and volume in all registers
• Pink Gold Plate: Mellower with rich core sound
• Gold Plate: Rich tonal harmonics and depth

The attachment between neck and body is a core acoustic nodal point on the Saxophone. As such manufacturers are experimenting with applying different weight to this point. Some use heavier 'collars' on the body here, some go lighter. We've also seen the introduction of heavy weight screws to add stability to the tone and perhaps an extra weight to the sound. 

These things are difficult to quantify, what we can say is that you definitely feel a difference when playing vs a normal neck screw. The two optional weights allow for a lighter or heavier set-up. We'd certainly say if you're sensitive to your sound and how your resonance and resistance is set-up then we'd encourage trying one of these to see if it adds a little extra.