Levels of Distractibility: Who cares? = *. Some people will be distracted from your meaning: = **. Many people will be distracted from your meaning: = ***.
Question: "One of the few who (is) or (are)...." singular based on "One" or plural based on "few"?
Answer: I'm not sure everybody agrees with me on this. Plural. Based on "few." "Who" is the subject of the clause that follows "few," relates to "few" and therefore is plural. "She is one of the FEW who ARE experts in understanding statistics."
Rating of Distractiblity: *. Frankly, both usages sound correct. In fact, using the singular sounds more correct than correctly using the plural. I don't think many people will notice. Be more careful, though, in writing.