I have some personal experience and have done some reading and research on Fibristal:
I have one fibroid (~6-7 cm) and have done two 3-month courses of Fibristal over the last year to try to shrink it. Unfortunately, my fibroid did not respond. No shrinkage observed on the sonos done before and after each course. Two REs have recommended against surgery if I want to preserve my fertility due to the location of the fibroid.
I have scanned at the anecdotal experience (internet forums where fibroid patients taking Fibristal (Esmya in Europe)) and scientific research behind Fibristal (generic name - ulipristal acetate).
From the anecdotal experience, it appears that the drug does work for most people in shrinking the fibroid or stopping heavy bleeding/period symptoms associated with fibroids.
In Europe, ulipristal acetate has been studied and approved for 8+ years. There are journal articles authored by Jacques Donnez et al., called the Pearl I-IV studies. The Pearl I study shows that after one 13 week treatment - the fibroid volume decreases by 21%. The Pearl III studied 4 repeated 13 weeks of treatment, the fibroid volume size decreased 45, 63, 67, 72%, respectively. The studies followed the subjects up to 6 months following the treatment and did not see any regrowth but the medical research does say that fibroids feed off estrogen and progesterone hormones and will likely regrow.
In terms of side effects, these were fairly manageable for me. I took the pill at night and had some headaches. My periods ceased but one month, I did spot and have somewhat of a random period. I found the drug also knocked me out at night, I slept very well and felt very tired/groggy waking up in the mornings.
I hope all goes well. Take Care.