I upgraded from the 3D to this Rumblex Plus 4D and all I can say is WOW!!! This thing is incredible!! I wasn't sure if it was going to be worth upgrading but I am so happy I did. This machine is tough and has so many options. If you are on the fence, don't be! Just get it!
So far, after 2 days of using it I can fell my muscles are at work. Will come back with detailed review in a month with numbers as well (weight, waits circumference), So far, thumbs up!