Well, I feel a little bad. I asked for advice and for the first time didn't take it. Sorry, and thanks to those that did reply.
I found a place called PowerTrucks that is about 2 miles from my house. I went and had a chat with the owner, Paul. He took me through how the map is modified and confirmed that the mods would not change the way the ECU runs any other functions.
All my questions were answered. As I was driving to Ireland over the weekend Paul said to try the remap and if I didnt like it he would give me my money back and reload my original map.
So, how does it feel? well its like driving a fast car, jeeees its quick even with a caravan it really picks its skirt up.
MPG was up from 18 mpg to 19.5 -20mpg Not a masive improvement but the route was quite hilly. The auto box didnt need to shift down on most hills and when it did 60mph was maintaned.
I did 500 miles since Friday and took the van into the local Mercedes dealer today for a service, appart from the oil change the only fault is the diff input seal is weeeping, so I will do that ASAP.
They checked the ECU for faults and none came up, so very happy.
I'm hoping to get the van on a rolling road soon just for a power run, there is one local to me so I need to see if they can get the van on it, if I can I will post the graph.