Taylor,
When you use ferric nitrate, no matter what you use it on, you still have to heat the stained object to force the nitrate to combine with water, making nitric acid (HNO3) that can evaporate from the stained object. If you don't, the nitrate will remain in the stained object and, over time, absorb water vapor from the air and turn into nitric acid. That nitric acid will corrode almost everything except gold and platinum.
Using vinegar/iron stain the vinegar (acetic acid) has such a high vapor pressure at room temperature that no heating is necessary to drive it off the stained object. Therefore, little, if any, corrosion will result.
Best Regards,
John Cholin