I have regularly used these three (as available) in our diesels...
Wynn's Diesel Fuel Treatment (1-litre fleet can)
3CV Diesel Treatment (1L)
Miller's Diesel Power Plus
All three appear to be identical products - details and MSDS sheets on the web.
The cetane improver is naphthalene.
Just done a 'quick hit' (1:200) dose on our 2003 RAV4 D4D as I hadn't used it for several months, and engine was sounding and feeling a touch rough and lacking low-down torque. Went back to decent running within a day - so something needed cleaning out!
Have been using these products for nearly 30 years now (BX19RD onwards), and always with good results - particularly quietness and extra low-rev torque. Normal dosage is 1:1000 for regular use.
Some allegedly similar products don't measure up though, and have been found to contain little more than regular diesel. Worth checking the MSDS sheets; if unavailable, be suspicious.
This is the Forum for all your Citroen Technical Questions, Problems or Advice.