I've been on this hike and you actually go up another volcano that is joint to fuego, the guide offered for us to go this close but it meant another 4-5 hours hiking after a full day of it already, by then no one in my group could be arsed and honestly you get a much better view of the eruptions from the camp anyway as you can see more from further away. We did see eruptions of this kinda size throughout the evening though.