Whats the difference? Well a lot actually
Bi-folds can be fully opened up the same as french doors, however Bi-folds can be made longer to really open up the back of your house & bring that sunshine inside.
French doors can also be opened fully to allow the outside in, just not to the same level as the bi-folding doors.
The Bi-folding doors are more costly than the french doors. Making the french doors easier on the pocket.
Both options have many for rather than against, it all really comes down to space, budget & also which option you perfer
Both options get the thumbs up by RB Windows