Can't say I noticed a difference in soot, but it does seem to reduce the amount of exhaust smoke emitted.
Forte products are normally only available to the trade, I know the local rep. so can get the odd single product rather than having to buy a full case, and the results from the forte diesel additive are certainly more immediate than the millers stuff. They have good documented proof of garages running forte oil flush before changing oil, then using a couple of quarter tanks of fuel with the diesel additive and it restores compression pressures etc etc.
I used the petrol additive in my 2CV and it seemed to get rid of a slight hesitation around 2k revs.
(I'm not in the trade and these are my completely non-scientific findings!)