One network, and it is the right one
France plans roam on Orange only. No SFR, no Bouygues, no Free Mobile.
Single-carrier roaming is usually a warning sign, because it removes the fallback you get when a plan can hop between networks. France is the exception worth knowing about: Orange has the strongest coverage in the country and its advantage is largest in rural areas — precisely where a fallback would otherwise matter.
So the trade-off lands well here. You lose redundancy and gain the network that has the fewest gaps to begin with. Compare that with Germany or Switzerland, where our plans route through the second and third networks rather than the leader.