I try not to buy every specialty ruler. I do have the tri rec, a kaleidoscope ruler by mart mitchell and a creative grid pineapple log cabin ruler. When I first started quilting I bought a 6 inch square and 6x24 ruler. The first specialty ruler was the tri rec and it was required for a block of the month class I was taking.
I was recently thinking of getting a ruler work straight line ruler for fmq. That also entails buying the foot. I'm very cautious to use a ruler fmq without the right foot, for fear of damaging my machine. I know if the needle hits the ruler it can really throw the timing of my machine off and that is an expensive repair. So I am so debating this as it becomes an expense being I have to buy the expensive foot for ruler work also. I only want it for straight line fmq. Curves and feathers I can fmq but those straight lines cause me grief. Suggestions

There have been many threads on here regarding rulers. My favorite ruler for cutting is the Oowhee ruler. I have their 6.5x24 inch and I use it every time I quilt. There has been very little mention about this brand in these threads. Their grippy backing is amazing. They also offer a service that you can mail them any of your rulers and they will apply their product to the back of it to make it nonslip, including your FMQ rulers.