SeLinux or Jail

In a forum post from around 2009, i read a discussion and opinion about using jails. My take on that topic was that using a jail is no more secure, indeed even less secure than not using them. At the time, SeLinux was put forward as the best option.

Moving forward to today, I now see we have a jail and that Selinux may break some apps and is therefore left disabled.

And yet, when i google jail vs selinux, i am finding posts suggesting to use both (selinux inside a jail)

So may i ask,

1. what should we be using where we have client websites on shared hosting?

2. what does the Webmin>System>Jailkit Jail manager actually do? (when i click on it nothing happens)