The only time I haven’t felt safe on a guagua is getting off on Duarte to catch a taxi.
But on the actual guaguas themselves, I’ve never felt unsafe. Unless there are holes in the floor and I’ve only been on them a handful of times.
Another spot on. If you're not careful and don't look, you run the risk of getting clipped by a moto. However, many guagua cobradores look out for you.