Thanks for the replies guys, very helpful.
Some comments on why I'd want it instead of relying on the dust extraction from my crown guard, well the crown guard that came with my Xcalibar dosen't have an extraction port on it, also most that do only have the small diameter hose.
What I like about this set up is that (as DaveL and others have said) it can be fixed to the table extension, wide and long guard that takes upto a 400mm blade, my saw is 300mm blade diameter, you can get it close to the work and still see the wood running through the blade, and last but not least it has 100mm dust extraction that will tie into my existing fixed system.
With the positive comments I've had I will be placing an order tomorrow.
Thanks again for all the comments.