Let's face it, entering the rebreather world is the start of something new. You already know how to choose an instructor for a rebreather course. If a student is to be well prepared to dive safely with a rebreather, such training, like OWD, should include a detailed theory section, pool training and open water diving.
The theoretical section ranges from about 8 to 12 hours where you will learn specific things about the operation of the device, its types and configurations, details on oxygen sensors, CO2 absorption, breathing work with the rebreather, etc. A very important chapter is of course physiology, which brings new contexts with rebreather diving, and it is necessary to be aware of new pitfalls thrown at the diver in the form of dangerous situations.
With a rebreather, for example, you can easily get to physiological gas levels that are not at all common in open circuit diving. Dive planning and gas management are also fundamentally different. A good instructor will put all these new facts into a coherent context so that you understand the issues well. This is the only way you will be able to make the right decisions at important moments in the future.
We've already written about instrument set-up, but there's no harm in mentioning it again because it's a critical part of training. A properly assembled and well tested apparatus before the actual dive forms a keystone factor of a safe dive, and everyone needs to be able to operate it without hesitation.
Training in a pool or confined water should give you a basic familiarity with how the apparatus behaves underwater. You will get a feel for it in a safe environment before venturing into open water. You will go through the most basic exercises and begin to learn the necessary habits. Usually, one training session in the pool is enough, but some training systems give even more attention to this part.
The core part of training, as with any other course, is training in a real open water environment to gain real experience. Given the wide range of skills a diver must qualify, a good course should include a minimum of 8 dives of 40 - 60 minutes duration. Anything less is insufficient.
During this training you will learn to operate the unit in detail underwater. Controlling buoyancy or maintaining optimum loop volume will be new skills. You will get the drill of closing the mouthpiece every time you take it out of your mouth into your muscle memory. The mask won't be the only thing you'll be able to pour water out of underwater because you'll learn how to pour water out of the breathing circuit as well. This and many more such exercises will prepare you for common rebreather diving situations. It would not be a good course if it does not also prepare you for emergency and risky situations. You will learn the procedures for dealing with failures or unexpected events such as high and low partial pressure of oxygen, hypercapnia and so on.
I dare say that after completing the rebreather course you will leave as a new diver. You will learn during the course that you cannot approach a rebreather in the same way as conventional open circuit, because it simply works on a different principle.
When you encounter an obstacle underwater, you'd rather swim around it than swim over it in one mighty breath and exhale to return to the original depth. You will already understand that, unlike the open circuit, ascending to the surface can make situations worse and that you have much more time to solve the problem underwater.