Most barbs are quite harmless. It is fallacy that barbs are nippy. A few species are aggressive, all the others, (100's of species), get tarred with the same brush. Another reason barbs nip is when they are kept incorrectly. Most barbs a shoaling/schooling fish. Kept singly or in pairs they show atypical behaviour as do most shoaling fish. They should be kept in groups, 5-6 ideally more fish.
Cherry Barbs are one of the commonly seen species which are not shoaling, 2 males kept together may fight. They are best kept as a pair or trio 1m 2f.
>>> I don't know why Pentazona's aren't more common
Pentazona don't travel well. The reason they are avoided by some importers is 100% loss in transit from the far east breeding stations are not uncommon. Once settled, they are a lovely fish. There are 4 sub-species.
Other harmless small species are Chequer Barbs, Dwarf Goldens, Green Barbs, (the real Green Barb, i.e. Barbus semifasciolatus, not Green Tiger Barbs), Black Ruby Barbs, Cummings Barb, the list is almost endless.