Mercedes Vito remapping - help needed please

[simac365]

I have a Vito 2.2 150BHP Dualiner which I want to get remapped. I have heard conflicting views on 'bolt in' units, The biggest problem with tuning units that are added on I've been told is that they only alter the fuel and can tend to make your car smoke on acceleration. A friend's Landrover garage has stopped using them and use a remap now as this gives better torque and well as acceleration.

Any advice gratefully appreciated.