We went with Seaduced last August - great trip. We saw bats in a couple of locations and we were able to look at them from as close as we wanted - like 12" away. They were hanging on the sloping ceiling. If your friends have problems with bats, they don't have to get close to them, but, they'll wish they did, because it was incredible seeing bats that close. We saw one female bat nursing a baby - it felt like being on "Animal Planet."
Bugs were not a problem on the trip any more than they were elsewhere in Belize. Just goop up first.
I don't know the distance of the hike, but, it was about 45-50 minutes, at a leisurely pace and level terrain. Crossed the stream a couple of times - wear sandals that won't slip off - through-the-toe flip flops may come off in the current, making for a long barefoot hike. In our group of four, we all wore shorts and tee shirts.
Seaduced accepts credit cards, but, like many AC merchants, they charge more to cover the service fee charged by Visa or MasterCard.
Most of all, take either a waterproof camera with flash, or else get a small dry bag with a neck strap for your camera (Sweetjane loves ziplocks, but, do you want to trust your Nikon in one?)