I hadn't done broad pen calligraphy in years, so I ordered a Mitchell nib, a Brause nib, and a Tachikawa nib for comparison. The Brause nib is SO scratchy. I suspect it's just that particular nib -- but I'm ready to take sand paper to it! Despite the bad experience with the Brause nib, though, I suspect if it's happening with both Brause and Speedball nibs, it is likely paper, ink or technique.
I agree with Linda and Heebs -- if you can get a parallel pen (or even a broad-nib fountain pen) to start with, that may be easiest. I learned with a fountain pen back in the day.
I'm also a leftie. I learned to write with regular nibs, but with my paper tilted 90 degrees clockwise. (So I am writing vertically downward toward myself.) Even with left-handed nibs, I find it works better to tilt the paper towards me some. I think it's worth experimenting with paper, ink, and paper angle.
Are you teaching yourself? What style are you starting with?