I've been on Hop-On Hop-Offs in a few cities. This one is sub par. St. Augustine is not that large, so you pass by the same spots several times during the single loop. I didn't learn much from this tour - the guide was hard to hear, and when I could hear, the focus was on jokes / questionable trivia and not on the important history of the city.
If you have young kids, just want a fun ride around town, and don't care too much about narration, you might appreciate this trolley. But if you want to learn about history, spend your time and money on a local tour guide(s).
Keep in mind that the trolleys get full and you might need to wait a while to hop on / waste an unpredictable amount of time (we waited for 45 minutes, then passed numerous stops where people could not get on). With smaller dedicated tours, you know when the tour starts, and there is always a place for you.
And, pictures I took off this trolley were not that great (when I walked around, I had much better angles, without being cut off by the trolley roof or neighbor passengers). Yes, the trolley takes you to a couple of areas that you might not reach by foot, but in my opinion, they will not add much to your St. Augustine visit / are not really worth seeing.