Yes it’s converts the 7+1 to 8+1. This dose not fit the 6+1 due to the spring is not the same as the 7+1.
It depends. I know, that sounds awful. It depends on the spring, it fits, but the spring may or may not be sufficient for locking the slide back. The solution would be to also swap out the spring, and install it at the same time. Of course this adds cost... But then you ARE getting an extra round. ;)