Pros
I've tutored for Manhattan Elite Prep on a freelance basis for about 4 years, and I've enjoyed the experience. They pay their tutors competitive rates, and most contracts (for the subjects I teach) range from 12 to 16 hours, which locks in a nice bit of supplemental income. I also appreciate the flexibility -- I coordinate all tutoring logistics with my students (while the company handles the administrative side). It's a comfortable arrangement, and I've always found them to be very reliable and responsive. Would definitely recommend.
Cons
As with all tutoring firms, there can be slow periods, so keep that in mind when planning/budgeting.