I used a birth stool with DD1 for the pushing stage of labour but as she was posterior it was the wrong position and I had to move her so had to get off and try a new position!

DD2 I never used one. I didn't feel I needed too, I found the toilet seat more comfy that time, lol

I was always reassured by mw that if baby came out while on stool that it would be ok and they would catch it