I've had no issues with Cthulhu, it just takes a sec to learn how to set it up.
It's mainly just a routing thing because you need to set it up essentially as a midi controller for the midi track so that it tells the VST what to play.
Step 1: Make VST track
Step 2: Make Cthulhu Track
Step 3: Set input on VST Track to Cthulhu
Step 4: Set input on Cthulhu track to keyboard
Step 5: Turn on input echo on Cthulhu track
Step 6: Play