Need a couple of better pictures to see if the nib is oblique or not.
Hold the nib to a light and look to see if there is a 15 degree cant to the nib tip. Would normally be a left foot....canted down to the left.
Either way, the semi-flex nib will be a lot of fun.
Don't push the nib more than 3 X tine spread over a light down stroke...........regular flex, semi-flex and maxi-semi-flex are in a 3X max tine set.
You need to go to Richard Binder's com, it is the Bible of fountain pens, nibs, filling systems, good advice on inks and many beautiful pens. It will take you some three days to read through.
There is an important article of metal fatigue from over stressing a nib.........especially with the even more flexible nibs.
After you get some experience, you will find you can find the limit to which a nib expands. In superflex a couple of pens from now, if a pen will max at a certain thing....such as my Pelikan 100n (A pen I never expected to own) it will go 5 X a light down stroke.....I strive to never take it above 4 X.
At first ...I am assuming you have a heavy hand....most do when getting into fountain pens, you will tend to max the tine spread often. After a while....took me three months, you press less and less.
A fine poster said, normal stubb and CI are 100% line variation, semi-flex (which is a stub nib) is line variation on demand.
The main trick to a lighter Hand, is to hold the fountain pen lightly, like a featherless baby bird.....
Don't make baby bird paste.
As mentioned before when posted the medium long pen is as long as a posted standard sized 400. The cap is longer so it posts longer.....same with the 100/100n and Ibis.
Posted the 140/400/600 have great balance.
I have a green stripped OB and a black OF...but my OF is easier to see that it is Oblique.