‘ve done 5 gorilla treks over the last 8 years, the last time I did two different groups in Rwanda and the Mgahnga group in Uganda. Every visit to a different group was a unique experience. On my first group visit in Zaire (now DRC) I was charged twice by the silverback (Ninja, RIP). After the second charge, he hid in the undergrowth and was not seen the rest of the hour. The second group in DRC had no silverback, but two black back brothers in charge (the silverback was shot by soldiers). On that visit a baby walked over and played with my bootstring until the guide shoo’ed it away!
In Rwanda, I saw one group that was out on an open slope which made for EXCELLENT pictures! The second group was SUSA and there were 36 gorillas in the group – you were surrounded by them! The silverback stayed in the dark bamboo and was not easy to photograph, but a couple females with babies came out in the open for great shots! Theyre were so many juveniles playing it was like watching a pre-school!
In Uganda, it took 5 hours of trekking to find the group. There were two sliverbacks and they passed within 3 meters of me!!! Incredible feeling! The group popped in and out of the dark and sunlight so photography was tricky!
My feeling is that you increase your chances dramatically of getting good photos or experienceing something unique the more often you go!
Finally, I have only heard of one group that did NOT see the gorilla group they were scheduled for (the Sabinyo group in Rwanda). The park allowed them to go again the next day or get a refund, so your reason for scheduling a second gorilla trek is NOT because you won’t find the group. The National Park service in each country monitors the groups daily and knows where they are. The Sabinyo group on that one day decided to move a long distance for some reason and the tourists just couln’t hike anymore that day (6 hours!). In Uganda, the UWA in Kampala will let you know if the Mgahinga group is in Uganda (so you can see them) or in DRC (when they will tell you to go to Bwindi instead)
