I posted this on Reddit but I might as well post it here, my current pens and what they're inked with and a sample of their writing:
Top to bottom:
FPR Indus demo, flex nib, J. Herbin Emerald of Chivor
Osmiroid 65, sketch pen nib, Noodler's Apache Sunset
FPR Indus demo, flex nib, Private Reserve Electric DC Blue
Pilot Metropolitan, medium nib, J. Herbin Bleu Pervenche
TWSBI Diamond 580AL blue, broad nib, Pilot Iroshizuku Fuyu-syogun
Kaweco Skyline Sport, medium nib, J. Herbin Ambre de Birmanie
Platinum Preppy, medium nib, included blue cartridge
Pilot Petit1, fine nib, included blue-black cartridge
Thoughts:
FPR pens: It's almost impossible to get all the water out after flushing it, even more so than the TWSBI. Gave both some initial flushing with water and filled them from sample vials, both started right up without problems. The line variation isn't huge but that's a thing with modern flex nibs from what I read, and I don't put much pressure on them either. We'll see how they hold up, but given I got them as a buy one get one free for a grand total of 23 bucks shipped, I'm quite happy with them so far.
Osmiroid 65: This came from a thrift store, a set of a drawing pen set, a lettering pen set, and a hopefully unrelated bottle of pelikan india ink. If it was used it was in the lettering pen set pen which belched some black bits that do not seem to be rubber but rather ossified ink and I haven't actually tried filling yet. Only one nib per set seems to have been really used; the copperplate nib from the drawing set is toast, one of the tines is slightly bent and they slip past each other if you touch the nib to paper, but the others seem to have been unused. The pen from the drawing set is the one being used here; it immediately started with easily dissolved old ink and seems to fill OK for now, but given the age probably needs a new sac desperately - The amount held doesn't seem to last long. But I may not be filling it completely either since I don't want to push the sac too hard, and it's a *very* wet nib that slaps down a bucketload of ink. The sketch pen nib was apparently never used as unlike the others it has a white plastic base which had no sign of staining and the flush was crystal clear. It has a bit over the top of it, flexes slightly, and is an absolutely lovely nib. I paid 10 bucks for the set, so I think I did OK there.
Metro: Not a lot to say. It's the basic starter pen and what I started with. It writes nice and smooth, but I wish the line were a little wider. I definitely prefer at least a western medium, if not bold/semi-flex. Need to try a stub nib. It's a little small for my big fat hands and the big dip in at the section is a little off for me. Not much to say about it lol.
TWSBI: This is a gorgeous pen. It holds wonderfully, the weight and size are perfect without posting, it writes well, I just plain like it. The nib does have a lot of feedback, not so much scratchy as it feels a little textured as it writes. It's not unpleasant and doesn't seem to affect the writing any, it's just not as smooth as some of the other nibs I have.
Kaweco Sport: I kind of hate this pen. It hates writing, starts hard, stops, etc. Not sure if it's the nib or the ink, the ink in the cartridge doesn't behave like the ink in any other cartridge I have from any brand or even the same brand. I kind of want to pull it out, hot glue it, flush the hell out of the pen and slap a different cartridge in and see if that helps any. It holds better than the Metro shape-wise but the weight is awful for me, it feels lighter than a ballpoint to me. It's also really ugly. I could overlook the ugly if it wrote better but as it is it sits there and irritates me. I at least didn't buy it, my aunt got it for me, but still.
Preppy: Surprisingly nice. The default blue is of course deathly boring, but what can you do. Writes nicely, it's a good size. Feels a little cheap but I expect this from a pen that cost less than four bucks.
Petit1: Also surprisingly nice. Only slightly longer than the Sport and thinner. Weighs about the same but somehow feels better in the hand, guessing it has to do with the cap not being most of the length of the pen. The proprietary to this particular pen cartridge is a bit of a derp, but nothing a syringe or just buying some cheap refills in Japantown won't fix. I like it much better as a pocket pen than the Kaweco, and if I lose it, like the preppy it's less than four bucks.
Yes, my handwriting looks like a demented six year old's.