I took it for a couple of years, with no discernible improvement. You aren't supposed to take NSAIDs while on Florinef, and I finally decided that I would get more benefit from the NSAIDs than I would from the Florinef, so I went off it (with Dr's consent & supervision). There was no worsening of the OI when I went off it, so I'd say it had no effect.
I've had more success with making sure I drink plenty of water and eating a high-salt diet.
Patients get truly varying responses to Florinef. For me it was just headaches and too high BP. The doc took me off it after 6 weeks. Others find it helps but have a lot of weight gain that doesn't disappear even when they go off it. Others find it helps.
If you take it, just monitor your responses and report them to your doc.
As Julia said, there are underlying factors to OI and sometimes we do better treating those. However, I think it is much more than HHV-6A--I've been tested for that, don't have it yet OI is a big deal with me. But, when I treat deeper causes, the OI improves a lot.