All three feature a smaller print area. Jr is the largest at just under 6"x6"x6". Simple is slightly over 4"x4"x5" and M3D is basically 4"x4"x4". I have a couple Da Vinci 1.0's that print effectively 7.5" x 7.5" x 7.5" and there are many times I need all that space. But there are enough times where a smaller bed would work fine.
These low cost 3D printers are making "a 3D printer in every home" more of a reality everyday. I know there are other printers in this low price category in the works as well. So it is still early in the 3D printer evolution and I'm having a lot of fun being part of it.