Pros
Randstad mainly does contract work which is generally short in period and depending on your field of expertise may or may not be a livable salary. These jobs can come from Randstad soliciting companies or the companies soliciting Randstad so there can be a wide variety of jobs. If you are at an entry level or an expert level you can find a job.
Cons
As an employee you are working for Randstad at another company. However you are being paid whatever amount Randstad decides because of the contract worked out in secret between the company and the Randstad (and pretty much all temp agencies). You can never see this contract. You will not be given firm hours or termination dates. You generally will not be able to start a contract with full knowledge of what the actual job entails. The duties listed in whatever job summary you are given are non-binding and are generally vague to begin with. Even if you're at a skilled job it is still possible to be asked to clean toilets. Randstad will also cover the bare legal minimum for healthcare coverage if you wish to join their plan. It is not worth it.