Terrible, especially if you do not speak Korean. They did not stop at the Tower and stopped at some dive by the river instead. On the rare occasions one could hear the recorded English narration over the highway noise, it consisted of minimalist statements like this is X bridge. The bus driver supplemented the recorded Korean narration with extensive live narration.
Unless you speak Korean, you’re on your own sight seeing in the bus. Driver didn’t speak English although locals were entertained with whatever he said. English overhead recording didn’t explain much so research ahead to enjoy the sights. We stopped at a bridge not at Seoul Tower for pictures.
What a disappointment! When I went to exchange my voucher for a bus ticket I was directed to the wrong bus and ended up taking a tour that was mainly in Korean so no headsets were given out. The English dialogue was minimal eg the next stop is.... and barely audible over the poor audio system. I also sat on the left hand side of the bus, while the main view was out the right hand side, so I had an obscured view for most of the trip I switched sides after a stop we made during the tour.
Admittedly I met some lovely people on the bus and the bus driver, who was giving the main commentary in Korean, seemed to be very popular with the people on the bus - so he seemed to be doing a good job. It was a bummer that I couldn't understand anything!
Just make sure you get on the right open top bus!