I totally get that the risk is usually low. However, on our trip, which we'd paid for a guide for, we crashed into a rock and the whole boat turned upside down. None of the boats without guides had this type of horrible incident.
My dad got stuck under the boat. No one helped him get out. No one even did a headcount. He managed to free himself eventually after struggling by himself, but a minute later and he would have drowned.
Although most trips will by luck turn out fine, I don't recommend going with a company that doesn't have adequate safety or scenario planning for when something can go wrong. They didn't seem to have a plan for if a boat capsized at all. They also had a light-hearted attitude afterwards, joking about the incident.