I tried carbon. But preferred the alloy one so that's the one we chose, plus it's a lot cheaper
I've been running the chassis for 2 months racing 2-3 nights a week and there is no sign of bending at all, we had another grade alloy chassis which bent almost straight away but this one has been fine. You can stiffen the car up by raising the carbon brace down the side but as off yet thee has been no need to.