This is a dip pen nib, you can not think of it in the same way that you think of a fountain pen nib. dip pen nibs are rarely tipped as tipping does not allow for the fine hairlines that dip pens are so good at achieving. Most dip pens are much sharper, and therefore much scratchier than what you are used to. A dip pen requires a lighter touch and different angle than a fountain pen. With a few changes in technique you will find it much smoother.
As to the flexibility, while even stiff dip pen nibs are usually more flexible than most fountain pens, not all dip pen nibs are flexible and as Mabie Todd was a leading manufacturer they made many nibs for general writing, which were not terribly flexible. The #4 is just the nib size, not the model, so your #4 may just be a general writing or ledger nib. If this is the case then you will be able to get some extra flex with a bit more pressure, but it will never be a very flexible nib.
As far as flow is concerned, there are many things that can affect dip pen flow. The most obvious is that oils from the hand and fingers can coat a dip pen nib and cause the ink to not flow properly. Cleaning the nib with some windex or alcohol, followed by a rinse and dry should cure this. The other big thing is that not many fountain pen inks work well with dip pens, they just aren't designed for this sort of use (many so called calligraphy inks are just as poorly designed). Using a reputable ink that is known to work well will with dip pens will help here, I would suggest a good sumi ink or walnut ink.
In any event, it is a nice looking nib and I am sure that with a few tweaks it will write nicely.
Here is a good site for dip pen supplies and ink:
Edited by jabberwock11, 29 October 2015 - 06:02.