The Reformer is my favorite Pilates equipment. Not only it looks sleek and beautiful, it is also the most versatile equipment in the Pilates realm. Exercises can be done sitting, lying down, or standing, and even sideways and upside down, although this last position is not recommended if you are just getting started on the reformer. You can exercise each part of your body dynamically, and you can increase the resistance, or add to the workout, by using the springs.
The benefits one gets from working on the Reformer in a class setting are increased strength, flexibility and body balance. However, the quality of your workout on the Reformer is ultimately the responsibility of your instructor. A good instructor with an eye on the details and safety and one who can cue you correctly can make a huge difference on the outcome of the workout. So, it is my recommendation that before you take a Reformer class make sure the teacher has many hours of instruction on the equipment and he or she has good experience.
Pilates, in general if done regularly, and correctly, helps to build the muscles of the core (abs, lower back, buttocks and thighs) resulting in benefits such as increase in overall strength, flexibility, coordination and balance which lead to better posture, more efficient movements from walking, running and practicing highly competitive sports and a sharp decrease in the likelihood of developing back pain and incurring in an injury.