I was considering using one, but after reading things like this:
https://www.subaruoutback.org/thread...roblem.378121/
I think it's best that I don't.
I have also read another thread, where a guy was told by a mechanic, that the valve will sometimes warp since it is brass, and it get's stuck, so to consider it permanent.
After all that info, I think I changed my mind, and I'll stick to the old fashioned way of removing bolt.