Just had a flight VIE-IST on one of the OS 738s (OE-LNS). IŽd advise against OS flights on these..
The seats (Y and curtain-C) are angled and curved in a way that at least I (185cm) had to sit bent forward or straight up the whole flight. Additionally, the padding is extremely thin - there are prints in the "padding" that reveal the metal frame and you can feel the exact extent and shape of the plate if you touch it.
I almost took the EUR150 upgrade at CI

, but my stingyness saved me from some disappointment
I guess this is one of the ex-Lauda planes? My other flights with (seemingly old) seats on the A320s/A321s were quite comfortable.