If the fit is spot on and it has some rubber cushioning on it then you shouldn't have a problem. There is no reason for it to be more rattly than a OEM bonnet as long as it fits right. It is very thin but very strong and the skeleton gubbins makes it very ridgid. The bonets I have had have mouldings/skeleton bits round the edges to give it the same thickness as OEM where it makes contact with the rest of the car if you know what I mean?
If you did have a rattle that you noticed it would be easily fixed by applying some 2mm heatproof foam tape in the offending area. I have done this with exhausts before but never had to do it with a bonnet.
You know the other option would be to wrap it in carbon effect vinyl (although a bit of a cheap boy racer option)