Hi folker,
we didn't use any external support tool as mainly we benefit from the unity editing features:
- Set up a UNITY grid snap of 0.5m or 1m
- Press CTRL + Drag the pieces you want to use (this will move the piece by the step configured in the snap param in unity)
- If there is any slight miss-adjustment press "V" and move the piece to snap it vertex to vertex to another piece
- Use the attached script to assist you rotate the pieces easily in steps of 90º (or the step you like)
The package is meant to be used like that and this tips should make your overall editing a lot easier
anyway, hope this helps :)