"Skype-killers" without end-to-end encryption are useless.
If they're based on WebRTC then I believe end-to-end encryption is baked into the standard. Whether they use the standard completely is another question.
I'm not sure that them having my messages unencrypted on their servers makes that feature any more desirable than Skype, WhatsApp and the like. Encrypted voice call is good, but in the case they don't say how they do that encryption, it'll remain less-than-trustworthy.