The only advantage I can think of with an open source crypto exchange code is the potential community, if there is one. The community can help address bugs and increase security.
This is also a potential disadvantage. With an open source code, a potential attacker could go through the code, find and exploit bugs that haven't been addressed in time.
So, even though open source is generally a great thing to have, with crypto exchange code, I would be careful because the devs may not be good enough or the community not strong enough.
I'm not saying that's the case here as I don't know RubyKube.