We read the Calculus Trap and intentionally slowed my son down a bit. He is 14 and finishing middle school and just finished working through AOPS Calculus.
I am not sure we would do things differently if we had the chance but some of the cons are that the school program will not be interesting if he starts doing AoPS, you will probably not get credit for some courses, it gets expensive to use AoPS, we had to get a tutor (initially more for him to have someone to "talk math" with but then because the problems were too difficult for us to help with, your kid will become very accelerated. Also, be aware that AOPS is pretty easy with the grading and I think that resulted in DS making careless mistakes. You get several chances at missed problems and it is pretty easy to get to the blue.
Our son really loves math so it has worked for us but it would be better if one of his parents was better at math and/or if we lived in a larger area where there were more kids like him around...
