Pros
Good for entry-level / temporary IT jobs, it will give you the experience you need for later as you progress in your career, collegial/informal environment, depending on the contract with the client was negotiated the pay and benefits can be acceptable or not, events and some "touch base" lunches paid by TekSystems. They offer an online course repository if you want to study on your own. Bottom line, if you want to work with them, be ready to accept the cons.
Cons
No career advancement, no assistance with IT certifications training classes (you have to pay on your own). You are not a TekSystems employee, neither a consultant despite of what they say (if you want to be a consultant, work for an actual consulting company). As a "middle man" they take a chunk of your real salary, benefits are subpar or non existent, they can nickel and dime you. You are just a warm body they profit from when you are placed in a contract (until they don't need you anymore), this is not an consulting or an IT company, they only do staffing. Once you work for an IT consulting company as a full time staff you realize how underpaid you were and how paltry your benefits also were.