As you probably know, lenalidomide (better known to most of us by its trade name Revlimid) has been a successful drug for the subset of MDS patients with "deletion 5q" syndrome. Researchers want to know the other circumstances where Revlimid can be beneficial, such as patients without deletion 5q, or in this study post-transplant patients.
The higher the clinical trial phase, the more likely that participants in the study will benefit themselves, not just contribute to scientific knowledge. Usually a Phase I trial is studying safety, side effects, and how a drug is metabolized and excreted, a Phase II trial is studying effectiveness against a disease (compared to "standard treatment" or no treatment), and a Phase III trial is studying dosages, but these aren't always the case. This trial seems to be combining these goals.
I think it's worth a frank discussion with the study sponsors about what they expect to learn from the trial and what the benefits vs. risks are likely to be for you.