Great review! But more importantly: $15.50 for a Waterman 100 year. Wow. You my friend, are one lucky guy. You also found one of the true joys of vintage collecting, great deals on great pens. Oh wait, you also discovered vintage flex... a two-fer!!
The flex in that nib looks pretty flexy. Keep playing with your handwriting style with the pen, those nibs are a ton of fun. I personally think that they improve your handwriting by slowing you down a bit and the shading they give off even makes my chicken scratch look semi-decent at times.
Anyway, congrats on a GREAT vintage snag.