There are so many factors to consider when buying a Magic Circle. Plastic or steel? What size is best for the majority in a group class? Are pads necessary for the inside as well as the outside? Check out the video for a breakdown of each feature to help you decide what's best for you and/or your studio.
Pads on the inside are not necessary but open up a range of exercises where your arms or legs are placed on the inside of the ring, pressing outward. It's a similar decision to buy a split pedal chair or only a traditional full pedal chair, like the Wunda Chair. If you're the creative type, go for inside pads. If you're more the traditional stick to what you know and what works type, go for outside handles only. They will be lighter which is definitely better.
The weight of the circle is a very important consideration. Heavy circles, such as 3-ring steel circles, can get really heavy quickly and trigger unwanted compensatory patterns. But if you have a really strong and advanced client or athlete, the lighter resistance won't cut it anymore.
Steel rings probably win in terms of longevity, although my plastic Stott Fitness Circle lites have lasted me for 7 years without any signs of wear. Good stuff.
14-inch circles are the most common size and work for most people. Smaller 12-inch circles are better, especially for lower body work, for short or small students, but might be too small for the general population.
Links to the Magic Circles mentioned in this post: