Pros
Demand offers an acceptable article-mill rate for writing ~500 word pieces and has a consistent and navigable system for writing and submitting them. The site eliminates the need to constantly hunt for work and provides a reliable pay rate and a client whose payments will not bounce or be retracted.
Cons
Editing is inconsistent and over the course of my 4 years of working there, requirements rose significantly. At one point there was a pay increase, but that was not always commensurate with the added demands. It's hard to be certain that titles are writeable and the work quality that was rewarded one week may be denied without payment the next. Standards for writers have also gone up, with DS requesting degrees and extensive work backgrounds for all authors, while only offering about .05/word.