I have the FA 35 f2 and I am very satisfied. I cannot comment on the optical quality of DA 35mm f2.4. I collected that the FA was a good lens and I chose that because of having a metal mount and being FF. In case Pentax ever produce one.
If you are interested to get the FA, you better check BH. The lens new at BH costs 399 $:
|Sadiqur_Rahman by Sadiqur Rahman|
from Ain't Going to Work on Maggie's Farm no More
|Airborne by John Beavin|
from - How to respect the Flag and Anthem - (Portrait in Full Colours + A Border)