It was sew "not easy" for me. Couldn't get it to work for anything. Couldn't keep it straight, etc. Maybe I just gave up too easy?? The best way for me to do half square triangles is to cut into squares and then cut into triangles and then sew the triangles together. I know it sounds lame (and a lot of work) but it's the only way I can keep my square somewhat "square".
I have since purchased the June Tailor Half Square triangle ruler and think this should work just fine.