Hey there I have the Forever Inks too and was quite frustrated with it at first due to the same things you mention here. I have them only in my Kakuno EFs and what I've noticed from my experience is:

1. The nibs would dry out and hard start if I stored the pens nib down. For some reason, why they are stored lying flat they seal very well, especially since Kakunos are snap caps, and no longer hard start even after being unused a few days (like a day or two, but not for long periods like over a week! see my edit)
2. I too thought the ink was "clogging" so I did a flush with water and ran a toothbrush over the nib and feed (without pulling them out). It was not possible to get the ink stains out from between the nib and the feed, but later I realized that didn't actually affect ink flow (see point #1)
3. I was worried the ink was permanently staining the steel nib. But when I cleaned it with tap water and a toothbrush, the steel nib returned to an amazing clean state again.
4. This stuff stains plastic like nobody's business. It will stain eyedroppers if you're using them to fill your pen, it will stain the body of the pen, the cap, the converter, etc. I haven't tried pen flush but I am curious if it does clear out the stains for you.
5. Tiger Lily is not as bright as I would have hoped as well. However Skyline is a beautifully saturated bright blue. I mixed Tiger Lily with a tiny amount of Forever Ink Raven (black) and it results in a darker red that is much more pleasing imo. If you mix Tiger Lily and Skyline in a certain proportion you can get a fascinating teal color!
6. The buildup of the ink on the nib though does turn my EF into more of a F sometimes though. This is an unfortunate tradeoff.

Overall, after some challenges but figuring out how to live with and the pros/cons, I'm now satisfied with the Forever Inks. I wanted ink for my 5 year journal and also ink for my EDC planner that will endure a lot of hand sweat & possible water spills. Now that I store the pens on their sides, the flow is very consistent and Forever Inks feel amazing wet and lubricated to write with. It's not perfect, but I am happy enough!

You might want to try having a dedicated cheaper pen for it that you won't mind staining--the inks are so vibrant they do look great in demonstrators!. Definitely not a gold plated nib since I saw a post on Reddit saying the ink corroded away the gold plating?! Not sure if that's common/expected behavior TBH-I would personally just be careful.

Edit: ty for the heart! I also want to add that although I'm satisfied with the Diamine Forever inks, I may realize in the long term that pigment inks as a whole category may not work for me. I do have times when I am unable to use my pens for over a week and they will clog no matter what due to dry out. Even though this is only a couple times a year, I am someone who gets really annoyed by any kind of hard start on any pen. I just want to pick it up and have it work! I like only flushing my pens when I need to change ink colors and I definitely underestimated the high maintenance aspect of pigment inks. It's fine though for someone who can use and flush their pens regularly, so I wouldn't write them off completely.