I haven't used it. But I have a curious fondness for these types of things, though at a much lower price point. Lensbay's, Diana's, Lomo's.... all that cheap crap. The crop on the bmcc seems to be a little prohibitive on their application in my opinion. The center sharpness takes up too much of the image and I feel better served using them on a 7d. The larger sensor just provides so much more out of focus area which is the fun part of this stuff for me.
They would probably work better on the BMPC or BMPCC with a speed booster than on my ef bmcc. I probably should change models eventually.
I will say however that this petzval gizmo looks like a gimmicky rip off. I don't need brass as cool as it may look. And I certainly don't think I've I've seen anything from it that looks anywhere near as good as lens baby footage I've seen.
Just my drunken sunday afternoon opinion.... My drunken friday opinions are far more lucid.