Could somebody kindly explain what would be involved (cost wise) once purchasing the kit? who sets them up etc?
Well to buy new costs about £160, for the basic kit, depending on the conversion rate at the time of purchase plus P&P. Second hand they go for about £85 delivered on average plus another £40 for the unlock key. Or some people will update the map on your car for you from £80-£135, this includes the cost of the unlock key, depending on where you are and who you go to.
Once purchased there's no additional costs as the maps, including updates, are free from fastchip.nl, unless you opt for a custom map...but I'm not sure if Henk does them any more or the cost if he does.
You set them up yourself using a laptop and the instructions ChrisPearson has posted, although you need to make sure you get the right .rst and .cal files for your ECU.
Risks, worst case you could f**k up your ECU and have to get it repaired or buy a new one. But I can't say I've read of anyone doing this and if you follow the instructions in the manual I doubt you'll have any problems, but it is your responsibility if you f**k anything up.
Gains, doubt you'll see big bhp increases if any TBH. But you should find the power delivery is better, especially mid-range, and if you go with the Group N .rst you'll increase the rev limit to 7,800rpm once up to temp; oh and a smoother idle than standard.
It's a good bit of kit for the money and recommended highly by nearly everyone that's used it.
Sy