Glad to have another broad edge aficionado on the Forum,
@ChessieHere's my 2¢ on broad edge nibs. Okay, I won't lie - I have a lot of feels about broad edge nibs, and I'm a teacher, and well... you asked.
Every broad edge nib (including fountain pen models) has some virtues and some drawbacks - I usually make the choice based on a variety of factors. I use them all from time to time for different projects. I'm going to focus on the ones you and
@Erica McPhee mentioned, with a word about broad edge fountain pens too.
Speedballs are fine - they're good for beginners, because they hold a lot of ink and they're easy to start. But they don't make super crisp lines. Also, the way the reservoirs are attached (and not practical to remove) makes them really hard to clean and dry thoroughly (which, er. I get it. I'm a little extra about cleaning & drying my nibs), so they tend to rust out faster.
Tachikawa (I assume you're talking about the C nibs) have chrome plating, so they stand up to sumi (and other highly lacquered and/or more corrosive inks) a lot better, but once that coating gets breached, it's all over. The under+over reservoirs really help you get some mileage with the very wide nibs (I don't really use the small ones), and you can feed different color inks into them to get some ombre blending. I know a lot of Manga artists that use them for lettering and for drawing, and when I use them, it's almost always for drawing, rather than for lettering. They can be hard to start.
Brause are oblique cut and pretty stiff - like Speedballs, they're good for beginners, the reservoirs help them hold a lot of ink, come off easy for cleaning, and they're pretty easy to start when they're new.
Hiro Tape Nibs (Leonardt) are not quite as stiff as Brause, but not nearly as flexy as Mitchell; also oblique cut. They're my first choice for beginners (except for lefties); they're easy to start without much nib prep. The reservoirs hold a lot of ink, meter out thinner inks well, and also come off easily for cleaning. They don't last long in certain types of sumi ink no matter how well you clean them though. I actually really like these for Italics (not so much for blackletter though).
Mitchell to me (and a lot of other broad edge calligraphers) are the gold standard - quite flexible and square cut (I prefer square cut), they feel and behave more like feather quills than any other metal nib on the market. Super sharp lines (and you can gently sharpen them as well), but a little hard to start. I hate the reservoirs and don't use them; they impair the flexiness, and make the starts even harder.
Mitchell Witch Pens! (which you didn't mention, but which I like a lot) - If you've never seen them, google it; it's easier than me trying to describe them. I'll wait. (
https://www.paperinkarts.com/miwipe.html). Super flexy broad edge nibs. And with these, the railroading is a feature, not a bug! A little pressure, and you have a split nib. Hairlines from the corners. Big reservoir built in. My go-to for making fancy blackletter capitals, versals, etc.
Parallel (fountain pen) - fantastically fun to use! I have them in all the sizes and all the mods (except for the oblique cuts). You can mix the inks by touching the nibs together or touching the nib to a drop of ink. Great for ombre effects, for inks with shimmer and sheen and duo-tone properties. You can refill the empty cartridges with a blunt syringe or mod the nibs into an Opus 88 body. Easy to mod, easy to use, easy to clean. SO easy to clean that you can use practically any ink/paint in them. even bleed proof white. even gouache. even Dr Martin's shimmers, as long as you pull the nib unit out and clean them out right away. Yeah - they'll never make a line as sharp as a Mitchell, but they do so many cool and fun things, and when you're working at a large enough scale, those hairlines need to be proportional anyway. Yeah, they look & feel like toys - I don't care; I stan Pilot Parallels. Fite me.
But you know - I also like those Manuscript italic/broad edge calligraphy fountain pens, and the Sailor Compass HighAce Neo fountain pens. They don't make as crisp and elegant a line, but when I'm doing layout and I just want to know my word/line count and get things drawn out, I don't want to be dipping all the time. Also, you can put fountain pen ink into them! We are living in a golden age for fountain pen ink, and the special features of contemporary fountain pen inks show off best in broad edge calligraphy.
--yours, K