Had the box for around 9 months now with no problems at all.
Occasionally I switch it down just to remind myself that it is working (very subtle operation) and also to remind myself how well it does perform.
The instant improvement in driveability and engine flexibility along with an increase in fuel economy is what I wanted from it. The idea to fit one for wheel-spinning performance is not what it's about to be fair (although it does improve it by around 25 bhp and a good amount of torque increase).
What it does do for example that the car (being quite heavy and lumpy) is much more flexible on acceleration from junctions, even in the wrong gear, jumping into lanes on motorways and results in a decrease in the amount of gear changing that I was having to do between the accelerating and waiting for the turbo to boost.
Here is a link to an article I wrote on the tuning box....hopefully you will find it useful?
http://www.drivn.co.uk/electronic-engine-tuning-guide/
p.s. If you are interested in buying one through DTUK....private message me and I may be able to provide you with a discount code for purchase.