My experience has been once you have a decent facing mill, the flycutter stays in the cupboard. The FM can take decent cuts but actually finishes better than a flycutter. It only makes sense, 3-4 times more cutters at work given the same feed, heavier tool, integrally balanced, typically more rigid because it fits the spindle taper socket, cutting geometry is always very close & consistent... Once upon a time one could say carbide inserts cost a lot more than HSS or carbide tipped cutters & you could utilize same lathe tools. But that cost gap has narrowed so as to be negligible. I have a 2" diameter 4-insert FM like Jangers middle picture, really happy with it. Inserts last a long time. I think its a good starter size because its in the range of what a light machine will allow taking heavier cuts. You can always just take stepped passes to traverse wider stock just like an end mill. But you can just as easily shave a thou off & get a wicked good finish to tight tolerances.
