It would be nice for someone in Europe to do a similar review of the European nibs.
... Bob categorizes the bowl nibs as mono-line writers. However, I have been able to get a slight about of flex out of them so my general writing is not a boring mono-line that looks like my fountain pens.
I can certainly run through a variety of vintage European nibs if there's an interest, but it'll take a while to arrange photos.
Truly monoline dip nibs seem to be rare beasties if my experience is anything to go by. There are plenty which are intended to be used as such, but very few which are firmer than a semiflex fountain pen nib. Waverleys, for instance, (with the turned up nose) were clearly designed with ease of writing on mediocre paper in mind rather than expressiveness, but once they've broken in they'll produce a fairly heavy shade if pushed - and spring back nicely. Bowls are definitely amongst the stiffer patterns, but they're not like nails. Stumpy little nibs like Wing Commanders are about the stiffest I've found ... they're generally italics anyway.
I don't think you can tell at a glance if a pen is going to flex easily, because as Christopher pointed out metallurgy and thickness are important factors. There are one or two promising signs though: long tines with deep slits on either side (which relates to Christopher's second point), and fancy eyelets both bode well. The real proof of the pudding only comes after a nib has been used for a while.