I have all the rulers. But my favorite is "Fit to be Geese". It's just for flying geese, about 4 different sizes. I got it from Debbie McInnis Thompson in Washington state. I had to get a special lesson on how to use it as I don't see some colors, but she helped me and now I can use it well.
I use the Doug Leko ruler a lot when slicing those corners off and it does save fabric. Sort of depends on the instructions and what the finished piece is. I have a lot less "do overs" when I use the ruler.