Well providing they can give you some pucker info on what the chip does then go for that.
All it should be doing is removing the 'Digi' lag by pulsing it's 'variables' at much more frequent intervals, and then add a more aggressive fuel and timing map for high octance fuel.
You'll only see an increase of 5 -10 bhp, usually around 7 for a stock engine - more if it's modded as the new settings will have a bigger impact; and when I say modded I mean head work / cams etc not a Peco and K&N !
The biggest difference is in the drivabilty - much crisper throttle responce and a nice power / torque curve will see you grinning

Before you spend yor money don't be afraid to ask questions of the seller! See if they know what they're actually talking about first ... last thing you want is to end up with a dodgy transistor chip that really does feck all !
Hope this helps ....