Do you mean Nandus spp. leaffish, or Pristolepis spp. leaffish?
The two genera are very different. Pristolepis are basically easy to keep and very similar to the African climbing perch in most regards. They're not especially aggressive, and only opportunistically predatory; their mouths are comparatively small, only somewhat larger than, say, that of a gourami. Kept with fish too large to swallow, such as rainbowfish, they're good community fish, and they're quite easy to feed on frozen foods as well as earthworms, river shrimps, etc. Once settled, they even take pellets!
Nandus are rather difficult to keep. They're more or less exclusively predatory, and have very large mouths. They much prefer live foods, particularly river shrimps and earthworms, plus, if you breed them, suitable safe feeder fish such as livebearers and killifish. They're not easily weaned onto frozen foods, and so far as I know, never take pellets. While possible additions to community tanks, their big mouths mean tankmates should be chosen with care, and they're sufficiently difficult to feed you may prefer to keep them on their own.
Cheers, Neale