I actually find the 144 most satisfying as a regular daily user. Small enough to go undetected most of the time, really easy to clean and change ink, and the smaller nibs perform admirably. I personally LOVE my Mozart but I know people might find it a midge small.
Are these pretty cheap to buy?
~ Seeing the 144 praised does my heart good.
Everything which gerigo has written is my feeling, also.
In classroom and laboratory settings, 144s are relatively discreet.
The nibs are nothing less than outstanding.
I use converters, rather than cartridges, and have never experienced any difficulties.
Are they cheap?
Well, I'm uncertain what price range might qualify.
Both new from a boutique, or pre-owned from various sources, 144s have seemed affordable to me.
They're fountain pens which never make much of a dent in my budget.
You want an F nib, which sounds ideal. As I've mentioned, EF nibs on a 144 are a joy to use, or at least that's been my happy experience.
As gerigo has explained elsewhere, she's found that Montblanc nibs vary in size, despite whatever they happen to be labeled.
In my case, the two 144 EF nibs are unquestionably EF size, which suits my professional needs.