I had my 1.9 jtdm remapped last week by Angel Tuning.
A chap turned up at work in his van, spent 20 mins loading software, we took it for a test drive and all was well!
The cost was £250ish, but this varies with different suppliers.
From his explanation the remap is a new set of maths data that tells the engine when to put fuel in, how much to use and what boost setting is required. He downloaded my current ECU settings, then uploaded the new data.
It was also stated that the remap is totally invisible to dealers/insurance.
It was all software, no hardware or physical changes at all. Although a new air filter or induction kit could be added as part of an upgrade.
Issues that seem to evolve from this type of work is a failing egr or dpf. This is in fact an issue that had or was occuring prior to the remap, the fact that the car is driven in a different way then increases the chance of these items failing/causing trouble. If you continue to drive as always, then all should be fine.
For me, I use Shell diesel, give the car a thrashing once a week and do around 20K a year. This is a great way of keeping egr/dpf issues from growing, keeps them open and used!
The change is not massive and instant. The car has a little bit more pick up in 1st/2nd, but the main difference is in 3rd/4th/5th/6th mid range grunt. The torque has been cranked up quite a bit, giving a lovely surge of power in the mid range.
The engine seems to rev easier and sweeter also.
Economy is supposed to increase between 10-16% according to the figures given. But this will take a few weeks to be seen, esp as I keep booting it at every chance!
For the money, it transforms the car to how it should have been. The figures look like this: approx 195bhp, approx 300+ lb/ft torque. And this equals
Hope this helps. By the way, get it done!