Wiki says that is became "the best organized and most effective of the French Resistance groups," so why hadn't I heard about them before?
At least partial responsibility falls on me not studying the French resistance much.
On the other hand:
The Francs-tireurs et partisans français[a] (FTPF), or commonly the Francs-tireurs et partisans (FTP), was an armed resistance organization created by leaders of the French Communist Party during World War II (1939–45).
That explains - or implies - a few things!