Since the thread was full of opposite views I thought I'd post support for this comment. Sounds like coming from an expert and should not need support but think of it a bit, an "ECU remap" can make genuine use of all the external sensors while an external box would need to try and fool sensor readings to reach similar behaviour. This is impossible already because the ECU often feels readings are in safe area while the combination is dangerous. In order to avoid this, external boxes can limit the change of sensor readings but then the effect too would be very limited.
Amazing how someone can think of an external box being better than an ECU program change (assuming both are properly implemented).
Personally I don't see any need for either one and I consider myself not biased but if I were to consider one, I would not touch the external box product.
PS. sounds like a bit of marketing from "ozmo" too, mileage gains should be marginal although some room exists when emissions are compromised.
Please tell me you got a remap and not some rubbish generic box ??
I've always had my cars remapped. Including an E320cdi which was truly a rocket ship afterwards. broader spread of torque, lots more of it and not gutless top end like it is standard.
Custom remapping your vehicle, when done by a professional, is massively complex. A generic cdi/tdi tuning box is a device simply used to boost certain available settings over the ecu - a general device and nothing more. They don't necessarily take into account the hundreds of signals an ecu processes. Crank some boost and over fueling is their reputation. Don't do it (!)
Proper remaps done correctly can be ghost-maps and are undetectable by dealers and insurance companies. They don't necessarily up or void your insurance either. You can have a choice of economy or performance remapping, or 'hard-map' ie for track days.
I've just moved to QLD from the UK and realised no one offers this service properly here and so whilst I'm cross qualifying as a lawyer, I've decided to set up my own company tuning vehicles.
This isn't a shameful advertisement post - far from it ! Although feel free to message me if you would like anything (we now do these awesome v-switch devises - not a generic box, but 3 separate bespoke remaps which constantly write to the ecu when the device is plugged in - this is very different to these normal plug in boxes. Ours is called the v-switch -- so the boxes CAN now be as good as a ghost-map but not a generic box)
But anyway - I've always had my cars done - I had an aggressive map put on my last A180 cdi with AMG everything inside and out. 180hp, 450 NM. 0-100mph in 20 seconds flat (down from 30!) so ignoring what companies suggest they can give you, it's more about spread of torque, throttle response and efficiency it will give your engine which in turn provides increases in everything. The A180 was 15 mpg up regularly on a 3rd lane very early morning commute after the remap too.
So - absolutely - get it done. Check out Viezu.com that's who backs me.