As they say in videos - you do this on your own risk. I wouldn't do it, at all. I'm even hesitant to get Iron Gall inks that ARE OK for fountain pens since even they need to be cleaned out regularly according to the makers of the ink to be sure nothing bad happens.
My main question would be why use it in fountain pens at all? Ink is fairly cheap, or you can find really good quality no flares everyday use ink around 5-10$ that will make it a struggle to end, so don't cheap out. You want to use this, get a fun dip pen and some different tips and fool around with instead. :)