I do like the flatness of the universal carrier. But there are no little posts or tabs with which to line up the negative, and when you bring the vanes up to the edges of the negative, they make the very edges of the picture a bit darker. And one of the vanes is a bit loose and moves around when the negative carrier is moved, which is a real nuisance.
I don't need 6x7. Just 6x6 and 35mm. I took a risk and bought a Nikot 35mm carrier for $15 this morning, it looks like it might fit, but who knows.
As for bar vs tab, all I can say is that the universal carrier is just like the ones right now on ebay. I'd say bar, not tab. I think the enlarger is called Rollei 67 XL, or something like that.