I install two of them in large, square, stone, 11th century franciscan church - feedback nightmare :) With old microphones I could't put volume up because of feedback, and people hear very pourly and there was lots of complain. PA System is 100V, with TOA amplifier. I upgrade system with dbx 131s Graphic Equalizer and Feedback destroyer. Still could't tame the feedback due the boundary microphones that priest put 1 meter from him. Nightmare.
Then, after a little reaserch those SHURE MX 418 D/C came :) With them sound/speech is very clear, much less feedback and most important: now I can put volume up. Lots of commendations came after install those mics. People can finally hear even when some babies cry during Holy mass :)