I was on it. I am no sure how to respond without writing a novel or scaring you. But I will try!
My experience of being on mag during labor was not fun at all. I was completely out of it, my body was on fire, I was hallucinating and at one point I had toxic levels and they had to stop it for awhile.
My experience of being on Mag during the pushing stage was pretty horrible. I was physically beyond exhausted at that point, and my central nervous system was depressed - it is what mag does to prevent seizures - which makes concentrating on pushing a stuck posterior baby out impossible, painful and traumatizing. I could not focus at all, I felt out of my body yet in my body, and it was all around rough.
I had specific complications though which added to it all being traumatic, so take my experience with a grain of salt:
I had central nervous system involvement with my pre-e, which is a step below developing seizures. I had bad hyperrelexia and clonus which indicate the brain stem is being affected/damaged, and my high pressures were around 180/120 while sitting up in bed. While laying down flat on my side they would go down to 160/100. So that was a problem. I never had protein in my urine, but the high pressures combined with the hyperflexia and clonus is what got me the mag. I know that what they consider to be high differs depending on you bp history. Since I had normal and low pressures my entire pregnancy, my highs were not good.
Jack was posterior. I mean really posterior. And since they broke my waters he was not going to turn on his own. And I was unable to physically get into a position that could facilitate a posterior birth (as in not on my back like I was - the worst position to birth a posterior baby in) because either the mag had depressed my muscle control so much or b/c when I managed to actually get to hands and knees, my pressure went up again.
I was anemic. Severely so when all was said and done.
I went on a mag dose high enough to need pit to continue to labor. And I got a huge dose of pitocin. They just kept upping it, especially at the pushing stage. And then my epidural stopped working (the bag of medicine detached from the catheter in my back). So at the end I was stuck on my back, with no break between constant pitocin contractions. And with every contraction and push, instead of Jack descending like he should, his head just kept grinding into my pelvis in such a way that he was never going to come out. WARNING I AM GOING TO BE BRUTALLY HONEST HERE: It was the most painful, god awful experience ever. I couldn't talk it was so painful. The pain was beyond grunting or screaming. I almost passed out it was so painful. I was one giant ball of pain. It was just a perfect storm. BUT on the positive side, that level of pain only lasted about a half an hour, and over time I have been able to block out the vividness of that memory. I really think that NOT passing out under those circumstances is a testament to how STRONG the female body is.
So my experience was what I would call pretty bad, BUT I had several issues going on. My pre-e came out of nowhere, I didn't have PIH first, my pressure got scary high really fast, and my cns started getting involved pretty quick too. But at least I didn't get seizures, and Jack was born healthy. If I lived in a different time I don't think we would have made it, to be honest. So for us the magnesium sulfate was unavoidable. In fact, it was a lifesaver. And it also gave me a chance at a vaginal birth, so I don't have to ever wonder if I did all I could b/c I know I gave it all my poor body could muster under those circumstances. And I am still here!
I hope you can avoid it, but if not, I hope your experience is not that bad. Chances are it won't be, I bet! (I wonder if you can just start the induction along with an epidural and then monitor to see if maybe the mag can be avoided. I was given the option of just inducing with an epidural before my pressures went really wacky since an epidural will keep your pressures down during contractions to an extent vs going au natural. Maybe ask your doctor about that option should your bp remain a concern). But if you do end up on mag I can make us a couple of "I survived magnesium sulfate" shirts

AND EVEN IF you do end up going on it, and the baby goes posterior, that doesn't mean your birth experience will be as traumatic for you as mine was for me. There are a lot of factors, and not everyone even has that hard of a time on mag (though it does suck for everyone to some extent). And I should also note that a 7lb 5oz, 20 inch baby boy in my tiny 5 foot nothing, size zero frame is nothing to sneeze at. For me, it was a hefty package I was trying to deliver. If it does escalate to you needing magnesium sulfate though, my best advice is to be completely open to having a very different type of birth then you envisioned, and watch out for pp depression afterward. I would not have handled it well at all if I hadn't let go of my ideal birth early on when it was clear it wasn't gonna happen. Since I wasn't holding onto that, I ended up with some really precious memories even amongst those unpleasant ones. Good luck! I will be thinking of you and hoping you have a wonderful birth experience. And if it involves mag at least you have somewhat of an idea of how it can go and hopefully your labor and delivery will still be pretty good!!