This is essentially an outsourcing company. When you work on a client side project, you have little actual professional interaction with Qualitest. This means you don't have a full employee-employer relationship with Qualitest, with all that would entail: training, development opportunities, an actual stake in the company, dedicated HR support, information flow/communication, etc. On the other hand, you aren't really an employee of the company where you are placed to work on a project, either.
As an employee, you are not disposable in that you do specialized work for a valuable client. However, your employment is not secure (it is project-dependent) and without on-the-job training, development and progression, you are not really building up or investing in your future career, beyond this particular role.
To make the most of working here, you have to work hard on your own time to continuously develop and make connections. If you are an ambitious high performer, you may not be adequately compensated for this (either monetarily or with praise and opportunities). Also, you will not have the safety (either job security or psychological security) that you may have as an employee at another company, as your position is more precarious - there is what seems to be a gross power imbalance between management as senior permanent employees with a stake in the company and the thousands of temporary contract workers who are indirectly employed, as the reviews here also indicate.
In short, working on client projects can be a good opportunity, but it is best to be aware of the company's model and the implications it has for the individual contractor (i.e. that they are not exactly an employee), and to be ready to work hard after hours to develop your own skills and career readiness.
