If an impact occurs where a plastic arm would have broken, then if you have an aluminium arm the force will either be applied on something else or the alu-arm will bend or break. Either of these cases will most likely be more expensive than replacing a normal plasticarm. I'll admit that the alu-arms look good, but they are simply not practical in buggy-racing. And you can normally get a whole bunch of plasticarms for what one set of aluarms costs.