Hi Ewan
I recently purchased the IQ-X and I can recommend it. I think it's as large an improvement over the IQ premium as the premium was over the 2nd generation IQ.
I can't comment as to whether it's the brightest dynamo light on the market as I only have experience with B&M lights, but in my opinion it's the best offering from B&M.
The mounting bracket that comes with it does not fit the Raven fork without adding a bunch of spacers though. I just used the metal bracket from my old lamp.