I have worked with this company since 2008 as a freelancer. I tell them how much work I'm available for each week and they send exactly that. They are very flexible, so if I need more money I take extra work and if I need a break that's fine too. They are super-friendly, always pay on time, and are supportive and understanding if I have a problem. I work from home at my own pace and set my own hours and deadlines. The pay is good and the work is interesting - I would definitely recommend working for them if you enjoy reading research papers in your field.
Cons
If you're inexperienced, you need to be willing to put in the time to learn the job initially.
I have been working here for over three years now, including a bit more than two years as a senior proofreader, and can recommend the company for its flexibility and consistency. Although remote, independent work is not for everyone, for those who prefer working from home and devising their own schedule, this is a good option to consider. I like the fact that I can proofread alongside other part-time jobs and tasks, and the company is very amenable to amending employees' workloads on request. A proofreader really is able to do as much or as little as they like on a weekly basis.
Cons
As may be expected, some proofreading tasks are more time-consuming or challenging than others, based in large part on each author's written proficiency, but that would be the case of any proofreading company.