i was worried if i should put the shimmer inks in piston fillers like my pelikan, and was afraid it would mess up the piston or something
I haven't had that problem. Remember, the nib units are removable, so you can flush the ink chamber out if necessary. But I also don't keep those types of inks in the pen for extended periods of time (any more than I would a pigmented ink).
I've also put shimmer ink in one of my TWSBIs, the 580-ALR with the 1.1 mm stub. And the only problems were that the ink (Diamine Arabian Nights) was so wet in that pen that I found that it wrote better with the nib upside down; plus of course the problem with the piston not extending to the back of the feed means that it's possible to get an air bubble in the ink chamber when the piston is extended as far as it will go.
Ruth Morrisson aka inkstainedruth