Just use MuseScore instead.
Can import from: MIDI.
tuxguitar-jsawas needed, otherwise no sound: https://askubuntu.com/questions/457321/tuxguitar-no-sound-in-14-04
Has OK step sequencer non-realtime up/down/left/right guitar based composition interface.
Has chord insertion.
Has bend editor.
Could be more amazing, but it is OK.
A bit limited by being very "guitar oriented". Shows you guitar strings, and you enter offset to each string. So to enter two adjacent notes you need to use two seprate strings and thing about the offsets. If only it had a more piano based interface.
Drum notation is also atrocious, you have to go to the top chord, and use high numbers starting at 36.