As far as I can tell, it's Thermacrom with niobium in the alloy mix insted of vanadium. The substitution is supposed to make the steel more corrosion resistant and easier to weld. I haven't seen hard data, so I don't know for sure.
I've seen two tubesets made with the stuff: Life and Spirit. The former is roughly equivalent to Foco in lenghts, diameters, shapes, and wall thickness and the latter is similar to Ultrafocco, so the weight restrictions should be the same. I should probably mention that with the Niobium tubesets only the main tubes are niobium steel, the stays are made of Nivacrom or Thermacrom.
As for mechanical characteristics, the Niobium steel is not quite as strong before welding as Thermacrom, but it has greater elongation, meaning it can bend a bit further before it fails.
I doubt you'd be able to tell the difference if you rode similarly designed frames made of Foco and Life or Ultrafoco and Spirit back to back. Neither will have a wieight, or stiffness advantage. And neither is likely to suffer durability problems in the hands of a competent welder.
So, yeah, go for the new stuff. It'll make your sponsor happy.