Pros
I could not come too much about pros. but if you are on a student visa, and you have nowhere to go, they could help you stay employed.
Cons
Their marketing team is not very helpful, you have to stay on the bench for a very long time to land on the client, before that you are paid very little. Even you are working for some client, they paid much less than you should get.Other vendors I know paid more than Marlabs. They promised to give you a percentage wage after working for a client for 6 months, but they will extend the period to 1 year. and they will calculate the percentage in their way and deduct at least 10%. if they promised 70% you will get at most 60% of the rate. and this "bonus" will not be paid to you if not ask for 100 times.