Not really. Clear text messages on Fb Friend List or G+ Circles are indexed and affects your profile (towards advertizers and others), whereas Neko.io messages are encrypted and truly private. Also, the Neko.io friend list spans across any and all social networks, so you would not need to maintain lists, circles, groups, flocks, etc in various services.
Can you use Facebook Friend Lists in Twitter ?
Obviously not. I believe Twitter is the only platform of the 3 that doesn't have a built in option to do this. It seems a bit like reinventing the wheel to me but perhaps that's because I can't see myself using it. I guess the USP is really cross-platform support?
Ok I see what you mean: circles. I agree that circles are old invention. But I think security of those circles is very compromised. I like the idea about encryption with social media.