I'm often asked about whether it's harmful for pens to use iron gall inks in them. For inks like Rohrer & Klingner Salix and Scabiosa - those seem to be more mild versions of the iron gall inks out there, so in my experience they behave close to traditional inks. For the KWZI inks, they seem to sit somewhere between the R&Ks, and something like Diamine Registrar's (which I've heard folks have issues with from time to time). I didn't have any cleaning issues with IG Gold, though I didn't leave the ink in my pen longer than a couple of weeks, and with regular use - which is about what I'd recommend with these iron gall inks before cleaning and refilling. If you're using vintage pens, especially with any kind of sac filling mechanism, I wouldn't recommend using iron gall in them. Vintage pens are much harder to replace, so maybe stick to traditional inks for those pens. I'm more of a modern pen user anyway, and in my experience as long as you practice regular pen maintenance, you shouldn't have any problems. If you're curious, Vanness Pens has great information on their KWZI page talking about the properties and warnings about iron gall use.
I enjoyed the color of this ink more than anything. It has a very retro feel to me, and is just different enough than a plain black ink to give your writing some character. I could have stood for it to write a tad wetter, but I don't think I'd give up on it just for that reason. Aside from buying straight from Konrad, you can also get the KWZI line from Vanness Pens here in the U.S. (60 ml for $14). I can't recommend KWZI enough - they have such an amazing variety of colors to choose from and from the ones I've tried so far, they perform very well.
Thanks so much for reading!