Went to a reasonably local place on a recommendation of my mate who has had his 320d remapped with excellent results.
Like many tuners, the guy offered try before you buy, so I did. He used Dimsport hardware and sent the map away a couple of times for 'tweaking'
Waste of time.
Got him to put my original map on, gave him 20 quid for his time (really nice bloke struggling through hard times!)
Went to my local shell garage, stuck a tank of optimax in and felt the difference.