No, we had no problems what so ever with missing parts of the itinerary. To the contrary, there were people on the trip who had originally said that they didn't want to trek to see the gorillas, but changed their mind. Gorilla permits sell out months in advance, but the guides did all they could to get passes, and they managed it!! So, absolutley no problems at all from that point of view.
I would recommend Drago. they do cost a bit more, but sometimes on a long dusty journey, the relative luxury of coach style seats, proper windows and decent tents at the end of the day is really worth it.
There's also security. We had a safe on the truck that our passports and large denomination dollars were kept in. The truck was also secure. I have no idea how secure other company's trucks are... I've not travelled with them.
As for the group, we were a motley bunch. As far as I can remember, there was us (honeymoon couple), a single travelling gap year girl, single travelling thirty something, a dutch couple, a canadian couple, an american couple, a Sri Lankan guy, and a couple from Hawaii. They were all so different, with a wide range of ages, personalities and backgrounds. So that was interesting in itself, everyone had different interests and appreciated different things.
Going on an overland trip is great, someone else worries about where to go, where to stay, etc. you just go along for the ride. but have you considered having a mixture of overland and independent travel? We stayed on in Uganda for another couple of months, it cost less, and we got to know the place where we were staying very well. we made some very good friends, who we're still in touch with six years later, and got a real feel for the culture, politics and day to day life of the local area. a much deeper experience. We also got some voluntary work and had the most amazing time.
the gap year girl on our trip also went on to volunteer in an orphanage in Rwanda for a couple of months, staying at a local family's home.
a mixture like this would keep your costs lower, and give you two very different types of experience in one trip.
where abouts are you travelling to?