Although I'll be in the minority (as always) I recommend staying away from Johnny Joint arms. The reason being is that the housing is very wide, and you don't get much misalignment out of them before they contact the mounting bracket. To make it worse, if the other end is pretty rigid, the can really stress out the mounts.
RK arms are great because the Krawler joints achieve high level of misalignment before contacting the bracket (if they ever do). Easier articulation and not as tough on the mounting brackets.
If you want arms that work nearly as well as any but require almost zero maintenance, look at JKS arms. Although right now you will have to mortgage your house to buy some. I've heard they are coming out with an equal-quality but less expensive version at the end of the summer.
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