Unlike some low-end junk (you find reviews on YouTube), it is horizontal at rest. I have not checked that gave the spirit level, my camera has an electronic level.
The only problem I encountered is that it is impossible to vertical (portrait) with super long and heavy tele zoom that is free of foot collar: the whole of the center of gravity is shifted to front, the single screw is not used strong enough and can not hold the housing that rotates slowly and the objective slumps. I doubt that another fastening system would have made a miracle, even on one foot ten times more expensive, the problem is clearly at the goal without collar. The clip is sturdy enough for μ4 goals / 3 lighter.
I have not tested it with a big SLR 24x36, I do not know if that foot is pretty hefty, especially vertically.