Stay away from aluminum A-arms and stick with RPM brand. Rpm is made of a very durable nylon material that flexes instead of breaking under stress like plastic. Aluminum bends and stays bent. You can go with aluminum bumpers with stock plastic mounts and aluminum bulkheads and chassis braces. The stock plastic bumper mounts will leave a flexing point between bumpers and bulkheads. Aluminum shock towers are also a good choice with the stock plastic body post. RPM just released their new tmaxx bulkheads and I'm sure it will be a good product to try vs aluminum also. Whatever you do for aluminum stay away from INTEGY brand. An aluminum beer can has more structural integrity. Stick with GPM, HOT RACING, FLM and any other quality brand of aluminum.
I honestlly dont know any cons to the rpm parts they are light not a whole lot more expensive than stock parts more durable and more flexible and not to mention can be pretty much any color you would like when you buy white ones. aluminum parts are heavy and once they are bent good luck getting it back where it needs to be and they are much more expensive than the stock/rpm and if you do decide to go with aluminum stay away from integy unless your buying like a battery box or something of that sort nothing movable that has a possibility of bending.
This is an example of possibilities of colors with rpm arms all you gotta do is get rit clothing die
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BTW a whole set of rpm arms can be had off of ebay for around 40 bucks aluminum arms are gonna run at least 80 to 100