Personally I would go for a tuning box from a company that has a decent reputation.

We have a plug & play black box on our RAV4 T180 that I bought brand new from our local Toyota dealer complete with a 2 year warranty that didn't interfere with the main manufacturers warranty so happy days

The figures that Toyota quote are an increase from 176 bhp to 218 bhp and from 300 ft/lbs of torque to 400 ft /lbs with increased MPG.

The car drove very well prior to the black box being fitted but the difference is night and day - low down in all gears it pulls like a steam train & is very noticeable in 6th gear if for example you go to overtake someone on the motorway - completely effortless. Just to try and explain how much of a difference it makes - I disconnected the box for a few days to check something out and my wife who is never usually bothered with this kind of stuff asked me what had I done to the car and when was she getting the extra power back

I was a little sceptical over the increased MPG but we have now put over 40k on our car since the box has been fitted and we are regularly seeing 6-7 MPG increase over what we were getting pre black box.

We paid around £350 for ours and for what we have saved in fuel it's paid for itself a long time ago.