I think SELinux is convenient or inconvenient depending on context.
For example on Android I find it's mostly convenient because it's been (IMO) well integrated into the system in such a way that I will only have to dig into it if I'm building a custom ROM or debugging an issue with native code.
I find the defaults on Fedora (and I guess CentOS also) to be pretty good as well, lately.
However I have my reservations about trying to implement it on top of any system that wasn't designed with it in mind. And it's important to think of each Linux distro as a unique whole system design in this context.
I have no idea how inconvenient it would be to try and start running SELinux on Ubuntu, for example, though I know there's support for it in the repos.
I've considered it, but it's like taking a vaccine where the side effects might actually outweigh the benefits, on consideration.