Hi Frenchi
To be honest, I don't think this is Micr. pt. 'Narrow'.........it looks smaller in leaves, and not so - well : "narrow".
There are really incredible lots of different varieties of Microsorum pteropus on the market, so a definite ID is impossible, from this pic, sorry!!
You can achieve this lok by using 'Narrow', though - but if you want even smaller leaves 'Trident' will be better. And I have to mention, too, that several miniature variations of Micr. pt. exist.
No Microsorum can be regarded "fast growing", but most will produce offspring on edge of leaves, identical to mother-plant. These can be carefully removed and placed where you want new plants.