Pros
Ulatus offers interesting work in various fields. I have passed their tests for Computer Science and Religious Studies, but mainly get work on computer science related academic papers, particularly machine learning. They have a wonderful benefit incentive program, where I can get a bonus if the quality of my work stays at a certain level, and a very good rate in general for most assignments. The project managers are quick in their communication. I also have a contract with them that guarantees a certain amount of work per month, which they gave me the freedom to set.
Cons
As with other translation agencies, there is about a two-month lag in payment. The average amount of head's up on assignments is usually either same-day or the day before, so it makes it hard to plan my work schedule. In some cases, I did get a few days' heads up. Also, sometimes I am offered pro bono short translation tests in order to win a new client, or translation quality assessments that are paid rather low.