I practice Baguazhang and here is what I look for. First thing I look for is what type of Bagua. Is it Liang, Yin, Fu and so on. Once I know that I can see if it really is what is being claimed or Karate with someone walking a circle.
Second thing I look for is circle walking. Are they following a good circle walk body erect upper body turned arm relaxed not tense is the foot work smooth or looks uneven and rough. You can really tell how good someone is by their circle walking.
Third thing I look for is the teacher. Does he present things clear is he abusive does his teachings contradict Baguazhang classics some teachers say do not walk a circle walk a square to me if that is the case we would not call it circle walking we would call it square walking.
Fourth application is the teacher just teaching forms or are you learning the "why" you do this. Some people think circle walking is pointless drill but it helps learn angles, how to enter and exit someone's space for example.
Is Baguazhang training intense? Walking correctly rooted in Baguazhang and walking circle for 5 minutes is harder to due then running for an hour.
Many times after Baguazhang circle walking I would have to sit down. As far as hard contact yes some go pretty hard and full out. Baguazhang in my opinion is very martial, deceptive, evasive to me I think of it as a ghost or wind one minute there the next minute the baguazhang person enters your space.
If your friend wants to learn more try reading the 36 and 48 baguazhang sayings they are similar to the Taijiquan classics. Also try to watch some Youtube videos to see the different Bagua flavors, Learn this history and distinctions that make each Bagua unique. Also try doing Ma bu, Zhan zhuang to help strengthen the legs,
walk around a tree will help you familarize you with the basic concept of circle walking and look for a good teacher of course!