Philosophical
Bagua's uniqueness comes from 'Circle Walking'. Whereas other martial arts like Tai Chi, Shaolin Kung-fu and Hsing-I can move in straight lines in all directions (forward, backwards, left right etc.), only Bagua practitioners walk in circles.
Bagua is a physical and energetic expression of the I-Ching (Book of Changes), a classical Chinese text. Through its practice, people can directly experience and manifest the nature of 'Change' (as depicted in the I-Ching) in the form of martial arts, meditation and energetic work.
Bagua's depth lies in it's circle walking practices; flowing footwork, coiling body movements, 'Static Arm Postures', 'Palm Changes' and continuous lengthening, twisting, opening, closing, spiralling and Longevity Breathing, all of which which fuse through internal connections in the body, making the body strong and open.
Martial
Bagua is most famous for being a martial art: "Bagua Zhang". Dong Hai Chuan made the art famous in the 19th century. The art had not before been seen in public and it quickly became known as the most effective system for self defence and combat, specialising in effectively dealing with multiple opponents attacking from different directions. Bagua Zhang became the chosen art of royal bodyguards in Beijing in the 19th and 20th century, and continues to be the martial art of choice amongst Chinese bodyguard elite today.
Dong had a handful of students who were already proficient in their own chosen styles of martial arts before studying with him. During their time with him, he taught them the art as would be best practiced by their own set of skills, experience and body type. Each of his main students became famous in their own right and continued practicing and teaching their own style of Bagua Zhang.
Dong Haichuan (though asked several times by his students) never fully revealed where he learnt the art, only that he was taught the art by two Taoist Monks on a mountain.
Monastic
The much older Taoist Monastic Tradition does not focus on martial applications. Instead internal connection, alchemical, energetic and spiritual purpose root practice. These deep practices are manifested through walking the circle and the Eight Pre Heaven Palm Changes. These were the original practices of Bagua Circle Walking in Taoist temples and remain so for the few remaining practitioners seeking spiritual development.
UK Bagua seminars focus on the Monastic Tradition and the Water Method as passed down by Lao Tse. The Water Method focuses on relaxing the body and mind and releasing stagnant Qi (energy) rather than strongly willing it to move. This method is more gentle on the mind and body of the practitioner, allowing their body to open and stretch safely.
Practicing the Water Method of a calmer steady approach means students will start their practices with slow steady movements and will maintain correct alignment and relaxation throughout their walking. Only after their bodies are able to remain fully relaxed and naturally open will they find they are able to move at faster speeds whilst remaining entirely aligned and connected throughout every moment.
This is different to some schools which teach Fire Methods, where the students can be taught at a faster pace and faster walking methods. Fire Methods teach excellent content however the relaxed energy and stability are not the primary concern, which may mean their bodies may not be not strong and stable enough to retain internal connections (throught walking) at the beginning stages. This is not suitable for everyone, including those with previous injuries to the legs or back. This can lead to the nervous systems becoming unstable and tight, causing tension and stress.