Having had intravenous iron infusions three times, approx 6 months apart, I have to say that they did not solve the problem. Iron/ferritin went up marginally for a couple of months and then I was back down again. Never felt a surge of energy or other noticeable benefit.
I did have a reaction, breathing problems and dizziness, on the first attempt, but was administered oxygen, antihistamine and steroids and was then able to tolerate the treatment. Had to have antihistamine and steroids on subsequent appointments.
The answer to resolving my iron deficiency proved to be Optiferrin+C which is the first iron supplement that agreed with me. Maybe starting probiotics around the same time helped.
I was very disappointed that the infusions did not work in my case, as had high hopes when offered them.
Wish you better luck,