We booked the two hour tour of Capri/Blue Grotto. It's €23 pp for the tour and another €18 pp for…read morethe Blue Grotto. It seems all the bad reviews are because people are saying they thought the Blue Grotto was included in the €23, but it clearly says that it's a separate purchase at the site, when you are buying the tickets. We went at the beginning of April and it was the first tour of the day, so we didn't have the peak summer tourist wait experience that a lot of the reviews say. We got to the meeting point at 9:20 for the 9:45 tour. We decided to purchase tickets on site instead of online because there's a chance you won't go to the Blue Grotto based on the weather conditions that day. If you buy online and the Blue Grotto trip is canceled, you can't get a refund - but you can move the ticket to another day. But we had a tight schedule and there was only one day we could go to Capri, so we decided it was best to buy on site.
The tour takes you around Capri, including the Faraglioni (the famous rocks), then to Blue Grotto, and back to the meeting point. We decided to just get off after the Blue Grotto and take the bus back into the other side of town, since that's where we wanted to go anyway. This saved us probably 1-2 hours of time. Overall, the tour itself was just okay but most importantly, it got us where we needed to go, and we saw what we wanted to see. So if you're strapped in time in Capri, this is a great option for you.
Tip - people basically bum rushed us to get to the top level of the boat. We ended up sitting on the first level on the left side in the front, which is outdoors, so you still get great views. When it was time to transfer boats to get to the Blue Grotto, it just so happened that we got to get off first because that's where the ladder was. So the people who bum rushed us at the beginning ended up being last in line and probably had to wait at least half an hour. So it looks like we got the last laugh.