Apparently it uses two cutting heads, interlocked like gears, to bore double-barreled tunnels over a narrower area and ostensibly with less waste. The tunnel takes the form of union Venn diagram, with a line of columns in the middle.
For tunnels, it’s not an unusual configuration. Tunnels are round because it distributes weight forces efficiently and because a rotating cutter head involves the fewest moving parts. But, this also often leaves space that’s hard to use, since most vehicles are rectangular in section. Intersecting the circles creates flat sides and reduces waste.
The Lexington Avenue line tunnels on the Harlem River are built this way. The deep-column stations of the former Soviet Union are constructed by tunneling out a larger chamber between two tunnels. See Mayakovskaya, for example.
But as far as I know, TBMs like this are rare. A technical paper I found explains some of the difficulties, but there are TBMs with 40- and 60-foot diameters, such as Bertha, used to tunnel the Alaskan Way Viaduct replacement, or what Tysons Tunnel proposed.
I have no idea about the feasibility or actual value. I’d love to find out more.