Pros
Lot's of job opportunities with new jobs added often in tons of fields and categories. Fairly simple application process with AI help for cover letters. The monthly fee includes credits you can use to apply for jobs. Decent help and communication from Upwork support and management. Options to pay extra and have your applications and profile boosted. Free help seminars to help with marketing.
Kontras
Recently, much of what I described as a Pro has deteriorated a bit. It still takes a good bit of time to custom tailor a cover letter that, more often than not, gets no response at all. There's a free level but you really need to pay the minimum monthly fee to have a shot at decent results. There is a fee to apply for each job and you'll find yourself constantly buying more credits every month to keep up with new job posts. Unfair competition has resulted from Upworks feature allowing applicants to pay to have their application appear at the top of the list.