Pros
The working hours are relatively short (at least for First Officers who have not yet been line-qualified).
Most of the time, the tasks are simple and easy, with little to no pressure, discomfort, or unpleasantness.
Under these circumstances, the effective hourly pay is actually higher than after formally line-qualified, since you are paid a modest but reasonable amount for doing very little actual work.
Cons
The training process feels oddly disorganized and ad hoc, lacking both systematic design and standardized flow.
It is difficult to understand how safety performance is reliably maintained in such an environment, which appears fundamentally unreasonable.