Reform Sex Offender Laws are more directed to the laws of for legislating registered sex offenders who have been adjudicated, served their sentence, and released into the community. NAMBLA is directed more toward the legitimization and legalization of sexually abusing children. Two huge differences, in my opinion.
(DISCLAIMER: I know Janet Bellucci, president of California branch of RSOL, in her association with my family friend, a sex offender registration officer for the Sheriff Department in Ventura County, CA. I don't agree with some of her politics, but I can unquestionably state that Janet has no affiliation with any member who actively supports criminal acts against children, or any other victim. That includes her staff.)