Review (3/5): Definitely not universal, but great if you have a dryer that it fits
I don't think this item should be marketed as a "universal diffuser." I tried it with a mid-range Remington, a high end T3, a mid-range Conair, and a low end generic dryer. The only one this diffuser worked with was the Conair. Unless you have a BIO IONIC dryer you run the risk that this item will not fit your dryer.
When I finally found a dryer that worked with this diffuser, the diffuser worked well. This diffuser is very well made compared to the diffusers that come with most dryers. First, it's larger than typical diffusers. Second, it swivels to open and close the air vents. I find that it's best used when my hair is nearly dry to put the finishing touches on. I was a bit skeptical of what a diffuser would offer at this price point, but I think the build quality warrants the price.
Overall, I proceed with caution when ordering this product unless you have the BIO IONIC. If you do own the BIO IONIC, this item is fantastic and I highly recommend it.