The RDA on Magnesium is almost never there on multivitamin formulas and so should be added separatedly, I can't really feel that (significantly) it helps for anxiety or jittery though, same goes for theanine, in fact theanine makes my jittery/anxiety worse. Best for jittery/anxiety is taurine, at around 2 grams per each 100mg of caffeine, YMMV.
I've noted overall anxiety got noteacible better when I added DHEA, I'd guess due to changes in the cortisol to DHEA ratio.