There are a couple of issues here....
They do quite well in a smaller tank, say 1-2g, as the only fish. Lower flow. They MUST be able to reach the surface as they are air breathers. The live plants will not do much for them in terms of keeping the water oxygenated...well in that it is not needed for them really...BUT do not let the plants overgrow to the poiint where they hinder the fish reaching the surface. Otherwise they do very well.
Remember that people kept these in these "betta vases." There was LOADS of misinformation about keeping them in there:
1) They eat the plant roots: WRONG (though if you are starving...)
2) Use distilled water: YIKES!!! Terribly for a freshwater fish
3) The roots were often not trimmed so the fish couldn't reach the surface of the vase easily.
Many probably were deathtraps for the poor things
Otherwise they are very beautiful fish that are pretty easy to keep