Product review (3 stars): nice but not that big
The diffuser itself is nice and serves its purpose ... but, it is not that big.  I first bought it to be used with a tagine but when I got it I realized my tagine was a lot bigger than the diffuser.  My tagine is 14in and the diffuser is about 10in I would say.  I wish I had bought a bigger one.
I use it anyway and since I have a brazerie for the tagine, I only use the diffuser when I use the stove.  So, if you are going to buy this, be sure you take into account the diameter and what do you need it for.