Help - which tuning box

I am about to take delivery of a 2006 Freelander TD4 and plan to boost performance by adding a tuning box but I am confused by the number of devices out there making identical claims in terms of fitment and performance/economy improvement. The problem is which box and which price. They seem to vary between £69 - 250, see ebay, surely they all do the same thing using the same technique. Can anyone tell me their own experience of buying at both ends of the price scale.

Before you fit a Ronbox (the preferred one on here) make sure the engine is running perfectly first. Any issues it has (and the normally have some) WILL be highlighted by the tuning whether it be a box or a remap (my preferred option)