I have used both Bibler I-tent and the MK1XL and here are my thoughts on each:
Bibler Pro's: More solid in the snow & wind. The peak vents work better than the MK. The side wall guideout points are included with the tent (the MK does not, you have to order this as an option). The vestibule design (sold separately) is much better than ID. It does not have snow built up as much as ID. The vestibule door design is a lot easier to use, too.
Bibler Con's: Harder to set up because the fabric is so taut when I insert the poles, my least favorite is the corner buttons, you have to insert each pole tips into these small metal pockets.
ID MK1XL Pro's: Much easier to set up; no plastic clips (as mentioned from other post), no corner pockets. ID offers custom-made tent with different color and feature options. The standard tent floor is a lot thicker than Bibler. And last but not least, the MK1 is made in Canada vs. China for the Bibler
ID MK1XL Con's: The vestibule design needs major improvement. I actually don't like the vent tube that much. It does need more guideout in the wind since the tent is not as taut as Bibler.
About the breathability, Tegraltex and ToddTex are actually the very same fabric, both companies purchase their PTFE laminate from the same source. But Bibler I-tent seem to breath better because of the peak vent design.
Just my 2 cents. Hope that helps.