I used it... unh... three times. Too hard to get followers these days to lose a lot of them to have a boost. But for your "purposes", hell yeah! The easiest way to lose followers...
It's like years of work to convert them, then you use one option... they've gone.
I've used them in regions with large populations, over 95% following, large temples, top oratory skill and as an elder of the faith. Mobs would cause somewhat more deaths than in less-optimal situations, but otherwise no priest action did visible or lasting damage. So even if you'd get these followers, it wouldn't be any stronger than what you've seen yourself.
