Pros
Flexible scheduling for getting in your hours. Good bonus structure for those who produce well. A nice cross section of people to work with.
Cons
For a "research based" consulting organization, Gallup collects a vast amount of data that is obtained through inaccurate or irrelevant methods. Client customers are routinely induced into providing positive responses to questions that were not even pertinent to their experience. Thoughtful suggestions coming from experienced interviewers on how to improve the surveys are summarily ignored. Though the "heart" of the data collection process, interviewers tend to be treated as 2nd class citizens easily replaced. The hiring/training method for new interviewers is an epic fail with a disastrously low success rate. For various reasons, Gallup does not appear to want a "professional" interviewing group, but rather a constant parade of 20 hour/week people who work a month and quit.