It's really a fun app, just like FL Studio. There're even people
who're trying to rebrand and sell it.
Anyway, it's not really "simple". I've been arranging my synth
tracks all from within LMMS, including full support for my favourite
VSTi. And that was without any SDK very early on. That is why I don't
have Qtractor or Rosegarden in my workflow, and have grown accustomed
to managing MIDI with a separate app in an ALSA-only session.
With JACK and audio recording support, this will be just as
promising as Ardour 3.