“I don't know enough about the Front National to judge their similarity to the "real" fascists, but do you think it should be deemed a criminal organisation?”
Hard question.
I would say no, even if some members I spoke with when I thought it was worth to try were potentially dangerous. Well, they were openly true Nazi to speak frankly (reproduction of SS poster on the wall, hate for others races, religions etc).
But the movement as such doesn’t openly want to destroy the regime. Jean Marie Le Pen did calculated “coup d’éclat” about the Holocaust (detail of history) but I would say that no, in my actual knowledge, the Front National is not a criminal organisation.

And having spoken to others groups, in fact Le Pen is Socialist Social traitor.

I remember an interview of French Basque Nationalists wondering who was Karadzic and who was Mladic…