MDC makes a unit for the 450 and for the 451. Area 451 is only for the 451. Both are pretty good from what I hear. I have a 451 MDC unit myself. SmartieParts sells the Area 451 module, and they have great customer service (I got my MDC from them before the Area 451 was out). SmartMaddness sells the MDC now, and have been very good with my most recent order from them, friendly and responsive.