I haven't used any on my 05 TD4 yet, but only 'cos it's in England and I'm not !!! I have used it on my x-type (2.0 duratorq engine) for the last 2 years and you can tell the difference - much quieter and smoother with only 50ml per tank.
I usually use 50ml of Millers in one tank (without 2 stroke) to keep things clean then 50ml of 2 stroke oil (without Millers) for the next 3 or 4 fills. I use an old millers bottle for measuring the 2 stroke oil.
I buy the cheap
low ash 2 stroke oil from B&Q and it's fine. The x-type forum guys also specify low ash and not synthetic or other stuff and the jag runs beautifully on the 3/1 oil/millers combo.
Also, I use good diesel (Shell nitro or BP ultimate, I've never rated the Esso or Texaco fuel as good for diesel, but they are good for petrol). I used to work in the petroleum additive industry so I know this stuff makes a difference. Using good diesel you don't really need the Millers as the cleaners etc are already in the fuel (but they are not in supermarket fuel, or most diesel sold on the continent), but every 4th or 5th tankful helps get rid of any extra deposits from adding the 2 stroke.
The benefits of the 2 stroke are that it helps keep the expensive high pressure fuel pump and injectors lubricated, but the downside is (very slightly) extra carbon deposits which good fuel and occassional Millers combo help to get rid of.
If your car is high mileage and you suspect it's been used on cheap diesel then it may pay to use Millers or injector cleaner as well as the 2 stroke to each tank for a thousand miles or so to clean it up - coupled with an EGR blank/bypass. Alternatively, get it terracleaned - but this can expose hidden problems (leaks etc) which are blocked by carbon. If you want to go the terraclean route do some research as there are votes for and against. I'd suggest looking at the
x-type forum as there's lots of discussions there (you may need to register).
If you want to see the difference, run your FL on 2 tanks of cheap supermarket fuel to clean out any additives, then fill up with Shell Nitro and add 50 to 100ml of low ash 2 stroke (put it in before you fill up to get a good mix). You'll notice the difference in engine noise and smoothness within 50 miles.