Blood transfusions have significantly more potential adverse...

Blood transfusions have significantly more potential adverse effects that an iron infusion. Yes- iron infusions do require monitoring, but this isn't specific to iron infusions alone. In fact, many hospitals don't administer CT contrast unless a doctor is present. I remember going to CT scans after hours as a junior doctor, so that CT contrast could be administered. There are also many types of iron infusions. Ferrinject, for instance, can be given over 15 minutes, whereas as methods require infusion over hours.

Nothing has 0% risk, it's just about balancing the risk. The point of the trial is to show that the nanoparticles are safe in humans, not that they are devoid of any risk whatsoever. I'm confident toxicity is unlikely to be a significant issue. Look at something like CT contrast, for instance, it's associated with known adverse effects, including nephrotoxicity- but we still use it. MRI contrast is much the same.