Expensive, but good. Works reliably. But AF assist lamp is missing.

The product works reliably and as it should.
One star deduction because Canon - has built no AF illuminator - in contrast to the previous model ST-E2 and also for Yongnuo model. That's me from many mobile use situations where I often relatively little light spot have (weddings, events, events of all kinds). The drawback was indeed known me before purchase, but given the steep price and because Canon offers no alternative except the large and expensive Speedlite 600EX-RT, I do not forgive the full 5 stars.