MM is a lot brighter than opalec. MM can also run on single aa battery while opalec have to use atleast 2 aa battery. so, mm will eat the battery juice down to the very last ones. MM cost ~ 40, newbeam ~23.95.
The Opalec will give yhou 8-10 hours of constant light output. The MadMax will give you 2-3 hours of MUCH brighter light. Look in the Reviews Forun for runtime plots on these adapters.