Tuning boxes fool the ECU into increasing boost and fuel by providing it with incorrect (lower than reality) readings. 

 

This is exactly the reason I will never fit a tuning box to a car, I don't want my ECU fooled, I'd much rather get it re-mapped (Live re-map) to ensure things are correct.

Remaps provide more control but they still push the engine internals, turbo and injectors beyond manufacturers specs. Remaps generally provide more power because they push closer to the limits, whereas Tuning Boxes tend to leave more room for error. Both retain the ECU's built-in safety systems for detecting faults, and placing the car in limp mode should something go wrong.

Both have their merits, but given the exact same power outputs I would take a well-mapped car over a well programmed tuning box. However, tuning boxes are cheaper to buy, easier to remove, can have multiple power modes to select from, and retain some sell-on value. You can buy one, play with it, and decide to keep it or sell it for a small loss afterwards.

I have never owned a tuning box but did have both of my Subarus remapped with good results.

My wife's leon fr is remapped (revo stage1) and it's awesome fun. Not as much fun as the previous remapped focus st220 but then it returns almost double the mpg sorry she's happy with the compromise. If the octy was my car (i. E. I owned it rather than leased) , I'd opt for a remap. However, because it's not mine, i will go down the tuning box route should i decide to do anything.

Snet with speeling mistkaes from my phoen

On one side we have (in my case) the dealer who is hesitant (and in any case won't cover the warranty) and a leasing company that won't allow it. 

 

Maybe the chance things go wrong as a result of a remap are tiny, maybe they aren't. I don't have any experiences with it nor do I have the knowledge to draw on to make an educated guess as to the possible risks.

 

I have to default to the knowledge of other people because I lack it myself and at this point I deem the risks not worth taking, simply because I cannot get a proper feel for the chance the car actually develops an issue that could possible be caused by (or linked to) the remap.