I had ARM without pessary and it was the WORST thing to have done. Seriously. It was done without checking which way baby was facing (palpating me). He was, it turned out, back to back and that is probably why labour was taking so long (id been in pre labour about 48 hours at this point).
Midwife broke my waters and then left me saying she'd be back in 4 hours.
Utter, brain warping agony followed, as waters were no longer cushioning cervix abd baby couldn't turn, so was squeezing nerves in my pelvis (this was explained to me after I had him by a consultant). I didn't know it then but the pain I felt was NOT normal. I had no break in the agony either,. After three hrs of hallucinating myself out of the room the mw checked me and i'd not dilated a cm.
I was then put on a drip and had the baby 24 hours later after two failed epidurals, gas and air and finally a spinal block for forceps.
Breaking my waters was, in hindsight, the worst idea. Baby's head was trying to fit into my pelvis sideways and hitting the nerves and crushing them (I actually developed nerve damage as a result). The loss of waters meant baby couldn't turn so slammed down harder, the wrong way, into the pelvis. His being the wrong way was probably the very reason labour wasnt progressing.
I've been through labour again since and now know what contraction pain is meant to feel like. NOOOOO comparison.
Make sure the mw palpates first to check baby is in the right position.
In my second labour my waters didn't break (naturally) until five minutes before pushing so it's hardly a hindrance.
Also remember that due to NHS metrics, I've waters are broken they'll want baby out within 24 hours, ready or not, so interventions of necessary.