Years ago I did this snorkel trip and it was well worthwhile. I think the big difference between Ko'Olina and where this one departs is that you have to drive down the highway about four miles to catch the boat and it is at a public pier. It is not an area that I would go to at night, but you should be ok during the day. Just don't leave anything, and I mean anything in your rental car. Also, the boat at Ko'Olina might be newer and nicer. The higher cost covers the extra cruise time to the Makaha area, or northwest part of the island, it covers departing from a nicer area and maybe a nicer boat. In fact, check to see if the same boat pulls into the public pier down by Makaha. You might be paying the extra money just to depart from a nicer area.
We did see Dolphins and the trip was fun. I would recommend it. But, which boat depends on what you are looking for.