Hi everyone, I've been looking at the range of tuning boxes available for the CDTI-150, but am confused about three things;

Firstly, there seems to be a huge variation in price. Some boxes can be found for less than £100 and claim to increase power and torque by 20-25%. At the other end of the scale there are boxes costing £300+, but claim only marginally better gains than the cheap ones (around 25-30%).

Secondly, in all cases these boxes seem to connect into the wiring to the fuel rail. Does this mean that they work simply by increasing the fuel pressure - for they clearly can't affect injector pulse duration from this location. This raises two further concerns for me;
1. If the fuel pressure is increased, does this put more strain on the pump, with the potential of premature pump failure?
2. I thought the turbo boost pressure also needed to be increased in order to provide enough air to burn the extra fuel. Surely increasing fuelling alone would result in excess soot and possibly damaged DPF?

Thirdly, Some boxes seem to offer switches to adjust the box settings. What is the benefit of paying extra for this feature?

Sorry this is a lot of questions - but I wan't to be sure before I spend my money and the commensurate increase in insurance premium!