The pen on the right is a Gillott 303. The one in the middle is an Esterbrook 048 Falcon. The beast on the left is an Esterbrook 340 Mammoth Falcon.
There's no way to really get the size across in pictures.
In the second picture, on top is a Wm Mitchell "G" which is similar in size to a modern Zebra G, on the bottom is the Gillott 303, and then second from the top is the 048 Falcon, which is normally considered a rather large nib, and the then Andre the Giant of the nib world.
These do not fit into regular holders. I just happen to have two very odd holders (modern plastic ones) without markings that they fit into perfectly. Very strange. These nibs are also rare enough that most people don't bother inking them up. But I had one with some touches of rust on it, and a holder that fits, so I did try it out.
Overall, it's a nicely fine and fairly flexible nib. But your hand sits so far away from the paper, more than a half-inch further than with a regular falcon, that you can't write with much control. I'm not even bothering showing the lame attempts.
I could see using it for off-hand flourishing, but writing is just too awkward unless you are Andre the Giant.
Anyway, thought I'd do a little show and tell of a rare and unusual nib.