I'm the guy posting webms in the thread, but to recap:
Rail spline points have erratic behavior at high speed. Levels have currently no limit on size and thus the background runs out after a time.
Additionally I found rotating to be a tad awkward. I kept deselecting the object on accident instead of moving or rotating it, though I imagine this control scheme works much better on touch. I understand only being allowed to have 1 uploaded level, but it would be nice to be able to save multiple levels locally. Audio sliders would also be appreciated.
Other than that its an intuitive and a open ended level editor. Had 0 issues uploading and downloading levels. I can see people making some crazy stuff with this.