I have the same ridge reamer that Challenger 1 has. On a re-ring job, I've always used it. In my cases typically I am re-using the pistons so the upper ring position is the same. I'll cut until I just reach the end of the ridge, then stop. Where I have seen people get into trouble is they start cutting the ridge out, get in a hurry, don't watch where they are going, and end up cutting into the upper ring travel area. Then you are screwed. As to 'belling' the bore with a ridge reamer, IMHO as long as it's above the top ring travel area and you didn't get carried away (looks like a funnel), who cares?

Now something that's other than a simple re-ring, well that's another matter entirely.