I've got a 451 and love it. Follow the directions and you'll be fine. 451 is less $ too if you're about saving $ even though it is about $15 under the other unit. That $15 is almost a tank of gas.
Here in a few months I'll be going for another cruise control unit. It's up in the air right now for what choice between the two. Leaning toward the MDC this next time around.
All that said - still love my 451.