I don't think you can assume any supplement is safe based on where you buy it, since the supplement industry is largely unregulated (thanks to our passing of the neutraceuticals act). You have to look to the quality control standards of each manufacturer and decide who you trust.
I also forgot to mention the kidney function issue, but figured ou were probably OK in that department. Just know, you can lose most of your kidney funtion before you have any symptoms at all, so get tested periodically.
Jan