Both great sandwiches, but different.
The PLOF is really misnamed, in my opinion, as it really isn't a facsimile of the Filet-O-Fish, what with the tomatoes and cabbage and the absence of cheese. No question, still very yummy, but not a classical riff of Filet-O-Fish.
The Little Tart Fish Sandwich, meanwhile, is almost an identical copy of the Filet-O-Fish, just bigger and badder.
Again, both great, just different takes on the fish sandwich. Sort of like cigars. Sometimes I want a classical Cuban, and I reach for the Epi No. 2; other times I want to stretch my repertoire a bit, and will reach for something like the Doble Cinco, which (while still Cuban in pedigree) is a much different take on the classical luxurious robust tastes of a traditional Cuban.