The versatility of a gymnastic ring cannot be easily measured. However, it is an excellent tool to develop upper body strength. Ido Portal, the movement Guru, seconds the same view about rings. Moreover, the unstableness of a ring is never hard on the joints. For example, performing muscle ups on the pullup bar the shoulders and the elbow joints can take a huge beating; whereas, a muscle up executed on a ring is easy and safe on the joints. On a different note, when you fail performing the prescribed repetitions on the rings on a given movement, it can be a very humbling yet enlightening experience.
On the flipside, a gymnastic ring was earlier understood to be used only by athletes. However, anyone can use it and benefit from them. A few benefits derived from the rings are strength, stability, and coordination. First and foremost, the instability of the ring is unmatched and requires more control, tension, concentration and effort.
Several other movements such as pushups, rows, dips, rollouts, and triceps extension can be performed. Believe me, for upper body strength, nothing can be as brutal and effective as a gymnastic ring. For the same reason, the gymnastic rings are used extensively at Ironcult.