hi Tek, there don't seem to be many Killi fans on here unfortunately but I've thought about keeping them before and would consider keeping them if I could find any locally. (my tanks pretty full at the moment so not immediately)
From what I found out during my research, although they are often kept in community tanks, they're quite a peaceful and adaptable fish so you should be able to keep them in a community tank with no problems.
I think they're like any other fish though, if you stick them with anything that will fit in their mouth it will get eaten.
I've also read that some of the species are annuals so only last around 12-18 months and can jostle their tank mates/each other so you need to be careful which type you get.
I think its like all fish to be honest, put them with fish that can handle themselves and they'll be ok. Put them with timid, small fish and you might have a few problems.