So I have used it personally and can speak to that; I also introduced it to a client when I worked at a domestic violence shelter and we walked through a tapping session for grounding during a panic attack she had.
My personal experience using it has been positive - I learned about it at the suggestion of my therapist. The first video I watched was https://www.youtube.com/watch?v=Sx0ydiRZoOk and I was convinced that there was 'something' to this method. Nick Ortner's book The Tapping Solution was another resource I encountered to learn more. In my own life, I have found tapping to be useful as an anti-anxiety grounding technique that comes in handy in a pinch - it's easy to go unnoticed or do a quick session away from others. I have also found it useful for processing emotions and experiences related to trauma, stress, and depression in particular.
I have not used tapping with other clients, but when I share the info with them I usually offer to send the above video first so they can get a sense of what it is about. I tend to also ask if they are interested in 'alternative or more holistic approaches' to their healing process.