Well, dual extrusion is not really that important, although the one in 3d builder catches my attention, my main consideration really is the quality and ease of use. I do agree that UM2 quality and reviews are really good, so supposedly the UMO+ should have the same quality or close to it.
For the 3D builder, there's only a handful of reviews on the 3dhubs and its hard to find pictures of sample prints, the primary reason I went to this forum and maybe somebody have both and can really compare the ultimaker and the 3D builder.
I am kind of leaning towards the UMO+ primarily because of the price difference (hope I will not be wrong).
Thanks!