Pluspunten
Studies are good for learning and improving skills. It is more of self training than earning money. Best give only one or two documents in a study as if you submit more documents, they will assign it a lower rating, giving them an excuse not to pay. The earnings come to 0.5 dollars per submitted document on an average. Maybe they are paying on the amount of documents submitted and not quality. One person got $50 USD after 200 documents and another dollars 50-100 after submitting 350+ documents.
Minpunten
Hardly any money or rewards. Lot of communication gap. What you want to communicate they understand opposite of that. Sometimes they are rude, impolite also will comment harshly on your submissions. If you submit too many responses to a study, you don't get paid. They ask for more submissions even after they are not going to pay for it. One person gave 18/25 documents correct for several studies, he did not get any money and they said his highlighting was poor. They use two excuses not to pay: 1. Document was not useful (Even after they accept is as useful). 2. Highlighting is poor. The only way to avoid it is to submit one or two documents at the most per study rather than having a waste of time spent on nothing.