I have had a few solutions on my DCi, standard at the mo though.
I have had a couple of remaps and a tuning box.
I'll start off with the box. It was from Dragon Performance UK, not sure if that's the same as Dragon Tuning you guys speak of.
Biggest pile of crap I've ever owned, shoddy design, and the fact it's simply boosting the numbers it's getting from the ECU before it passes them onto the common rail was a worry for me. It didn't touch the boost, which is a bit strange considering they told me the power gains would be on par with remaps.
After we installed it (took 5 minutes in fairness) and having the monkey at the workshop unplug it whilst the car was running, there were 3 stages of tune. 1, 2 and 3. I said put it on 3 as I'm not going to lose sleep over losing a few mpg from the current 50.
The test drive: Couldn't tell the difference.
Let's move on.
Have had a remap by superchips in which they did up the boost (can't remember off hand what bar it was before and after) which obviously allows more fuel which in diesel terms is more power.
That was a good modification. For a silly slow car, it was then slightly amusing. 5th wasn't dangerous for overtaking on shorter roads anymore, 3rd put the Clio 1.6 to bed and just gave an overall nicer drive.
I also had an Angel Tuning map. They come to you wherever you are, and also offer things like BMC induction kits yadda yadda yadda. I have to say it seemed to be the same sort of gain as the superchip, however they don't offer a warranty on the car. I also have a pretty good relationship with the people at superchips.
My advice. Superchip. If you're not worried about warranties etc (I wouldn't say there's any reason to be) and would rather have a £150 saving, for for an Angel Tuning remap.