I have i have!
Some things to note is that Fallen are cheaper than fallen with ALMOST all the perks of chosen thus they are somewhat better depending on your needs.
What do they lack? Legion keyword. Fallen can't ride vehicles sadly so get ready to footslog! If you aren't planning on running transports in the first place then chosen are cool beans but also keep in mind unless you bring Cypher you can't count on buffs.
I got down and built myself 10 chosen all of them with plasma pistols because you know...it seemed cool and they have a special rule that makes it all the more interesting.
I look forward to testing the list out, Cypher 3 units of fallen and 3 questor traitoris knights for a 2000 pts list.