I love the spool in my FTTC4 on the astroturf track we race on, it is absolutely ballistic off the start and out of corners

I've never had a problem with understeer, infact I had a HUGE problem with oversteer when I first put it in, my teammate had the same problem, I had to find so much more rear grip it wasn't funny!
I've never had a problem with durability, I've trained myself pretty well now to get off the throttle quick if it looks like I'm going to clip something.

I don't like it at our asphalt track though, made the car WAY to different from off power to on power, I'm much happier & faster with a diff.