Signal is, quite simply put, the second iteration each of Mr Acton's and Mr Benham's successful money-making trick, as the most cursory look at public records will reveal.
It is another start-up with completely vacuous claims about "security" and sporting an "open source" label because it looks fashionable, not that you can really do anything with their code apart from look at some version of it.
They are good at hype and that's why they're successful, but their product is exactly the same as Whatsapp in every substantial aspect.
Benham also did a chat at 36C3 about how great the centralised model is, etc. etc. It did not exactly go down well with the audience (it was really daft to try to sell that argument to a bunch of German IT people). The talk was at the conference website for a short while until Benham asked for it to be taken down, but can still be found on Peertube.
So TLDR: stay well clear of that signal thing.