Well, here are the options:

multichannel=True, sigma is iterable: works fine
multichannel=True, sigma is scalar: works fine
multichannel=False, sigma is iterable: works fine
multichannel=False, sigma is scalar: works fine

So I think it's fine! =) The only thing is that a user might forget to set multichannel. That's what *always* happened to me with SLIC (even though I coded it!) and what led to my development of `guess_spatial_dimensions`. But you don't like my functions so... =)