I went to San Diego on a budget so I decided to try the trolley, it was a good decision all in all since it gets to many places, some very far. I'm a foreigner so I didn't know what ot expect, but never had an issue. The trolley itself was for the most part clean, the people riding it just minded their own business, never felt unsafe.
The reason I don't give 5 stars is because it was a bit difficult to get the hang of it. Nobody explains you much, how the cards work, how the tickets work, the lines, etc. Basically you buy a card with a number of trips and you recharge it after they run out. Before you get into the trolley you are supposed to swipe your card in one of the machines at the station and then hop in. Supposedly there are people checking within the trolley if you actually paid but I never saw someone, of course if they catch you riding without a ticket there is a fine.
You can also not use a card and the buying machine emits a paper ticket, but of course this is for one way trips, while the card has other options. Also note that there are discounts for certain people.
Anyway if you are on a budget and don't rent a car the trolley is a good option to get around san Diego, just know that you will walk a lot because while the stations are conveniently located you still have to walk a good chunk to get to some places.