I also use IVPN, and I'm extremely happy with them. I used to use Viscosity to access them, but recently I've switched over to IVPN's own software. It makes choosing multi-hops easier, and comes with a option to block non-VPN traffic.
I get the open-source concern. I prefer using stock OpenVPN. But if you're going to do that, you need to manage your DNS servers, and firewall leaks. I'm not aware that iVPN provides source code. You could ask them.