The main advantage of using an editing and translation company over a freelancer or a friend is that you will get more than one pass over the document by a couple of editors. It will improve the language of your document quicker in most instances due to a checks-and-balances process that keeps the quality high. Conversely, with most freelancers, they are working on your manuscript as they have time and are less likely to do more than one pass through your document with a simple top-down process.
Word processing software like Microsoft Word means that anyone can be an editor, but it’s only training and experience that makes someone a great one. Your friend or a freelancer might give you a special deal, but how well do they know your research? Moreover, while you know they’re a native speaker, do you trust that they are a good writer? You know that there are weak writers in your language — English is no different.
Realistically, your average English speaker can’t justify why they write something a certain way, other than “it sounds natural”. For someone not in your field, a word might not sound natural simply because they’ve never heard it before! Moreover, the average English speaker will probably view your research in a country-specific way, whereas academics are exposed to ideas and collaborators from all over the world, and can better appreciate diverse perspectives.
Editors at editing companies like Uni-edit read and talk about academic writing every day, for us and for their research careers. We know how to express your findings in a field-appropriate way, so that you and your overseas colleagues and competitors are on the same page. Perhaps most importantly, we’re sensitive how English writers from different linguistic and cultural backgrounds express themselves most naturally: while our ultimate goal is to express your research in native and natural English, we retain the author’s wording wherever suitable because, after all, it’s your name on the paper.
Choosing an English editing company will guarantee that a professional editor, with plentiful editing experience and expertise in your subject area, edits your work. They will also ensure that the editing is done timeously (your friend might be busy, and good editing is time consuming). In the case of Uni-edit, they will generally also have two editors work on your manuscript, which ensures a much higher quality of work.
As Mark and Sally mentioned, a well-established English editing or translation company usually hires editors and translators from different subject areas; at Uni-edit, editors are also trained as a professional editor in addition to being a subject expert. Using a freelancer, such as a friend in the US, may work sometimes because of luck, but to be able to cooperate in a stable and timely manner could be an issue for the authors in the long run.
An English editing company has many professional native English-speaking editors who are trained specially to edit academic papers. A friend in the US is a native English speaker, but he/she might not have the same academic background as you. Therefore, I think it is safer for you to use a company for English editing or translation.
Using a freelancer or a friend in the US may offer a natural English speaker. However, I have experienced customers sending papers to us after a freelancer’s or friend’s editing. Most of the reason is not academic writing style or subject expertise. Uni-edit has different subject experts that can edit your paper based on the research focus of the paper, resulting in a more suitable product for journals.