I have purchased all the lovely Razer SWTOR products (don't judge) and once you've entered your code you get 2x +4 END Crystals per character you create (per code)... They are sent to your mail box
Just don't delete them (or replace them) as they are bound to your character and once they're gone, they're gone.
There was talk a while back about end level Razer Crystals but as of today's date nothing has happened... So, while the crystals are nice to begin with they rapidly become just cosmetic, rather than being much use. And yes, there's a VERY slight difference in shading to the advanced black-green crystal you can get in game... Not that anyone would notice! :/