only bad I know of is the tie rod extensions. Tend to bend alot easier than full tie rods. SOme have purchased a set of real plus 2 tie rods.
Also, you get bump-steer when full compressed, due to tie rods pivoting in a different spot than a-arms. In my opinion, If you ride really hard on rough surfaces, better options are out there. This is not a terrible option for the most part though.