So is the Ultimo new? Is it actually related to a 901? What are the differences between it and a 901? I ask because it is advertised as the new 901, but is not compatible with 901 parts. Also, I am interested because I may want one.

I just received the one that I won here. I know it says it's a new 901 but it is compatible with the 510. I have tried a 510 atomizer and it worked fine.  The cartridges I received with it were very different then what I was use to. They were exactly like a 510 wistle cart but had a foil covering on the bottom that the atomizer punctures when you insert it. I actually love this idea.   I have only tried it for a little while so will report back after a tried it for a couple of days. But so far no complaints on it

The foil controls the juice, when you twist it, you can hit another "Sweet spot, and it increases the draw.
 
Ultimo manual batteries,  work well on the 510, but are bigger. And the passthrough has a USB jack that helps prvent "line breakage", the #1 killer " of passthroughs