KDE Neon is basically based off on Ubuntu LTS. It's one of the main releases of Ubuntu. KDE neon is basically took it's main product "K Desktop Environment" and put in top of Ubuntu instead of the usual DE "Gnome".
So basically saying: KDE Neon is the same as Ubuntu. However there are some benchmarks that claim KDE Neon to be performing better than Ubuntu itself and even many other gnome environments.
In regards to bugs, there are regular updates that roll out. Im not sure about the frequency of it but i update KDE Neon on a frequent 3-2 day basis. The updates are well checked making it error free and stable unlike many distros.