I used bdring's extruder lever in my QUBD extruder for quite a while with mostly good results. I found however that it would catch on the raised area of the stepper motor and would not allow the bearing to sit completely tight against the MK7 drive gear that I use. With some filaments that ran a little thin, this led to slipping and clogging.

I also found that if I was using flexible filament, the space between the lever and the drive gear allowed the filament to get at an angle which led to it buckling and winding up all around the spaces in there.

This was my experience, I'm sure that others had different results. I decided to modify the lever to see if I could get better results. I expanded the curved opening on the back side more to make sure that it clears the raised section on my stepper motor. This allows the bearing to sit against the MK7 drive gear which has stopped me from having any slipping or clogging. I also stretched the channel section down to where it almost meets the drive gear which keeps the filament aligned straight into the drive gear. This has allowed me to run flexible filament without it buckling and winding into the extruder.