Clamps on and turns itself — useful if grip strength or the use of one hand is limited.
Standard can and jar openers usually assume two strong hands and a good grip. This one clamps around the rim and does the turning itself once it's engaged, so it can be operated one-handed without needing to grip and twist at the same time.
Make sure the clamp is fully seated around the rim before starting to turn — a half-seated grip is the most common reason it slips.