Pros
For the past ten years, Enago has steadily provided the majority of my income. They consistently send me interesting work. Sometimes the deadlines are tight, but I always have the option to refuse without penalty. The project management staff is responsive (available through chat). Payment is regular and transparent, and there is an incentive system to reward consistency and error-free work.
Cons
Recently, the workload has become less steady, likely due to changes in the industry globally.
If you your edits to a paper amount to less than 10% (or 20%, depending on the service) of the final document, it is sent back to you to make up the difference. Naturally, this encourages the editor to make unnecessary changes to meet the minimum threshold.
Sometimes quality reviewers make errors, either misapplying rules of English or through ignorance of what makes for proper academic English. However, they are open to discussion when challenged.