Bermuda snorkeling is great. I have never used any excursion on my three trips to Bermuda. We rent mopeds or scooters and ride down along the southern shore of the island. Horseshoe Bay, Church Bay, the area around the front of the old Sonesta Beach Hotel are all wonderful snorkel beaches. The beach areas around the vacinity of the Southhampton Princess are good locations. Since Bermuda usually does not have much wave action, you can see colorful fish all around the rocks and coral just off any beach.
If you get as far as the Somerset Bridge, just stop and look over the side of the bridge and you can see multi-colored fish without even getting wet. Have fun! Bermuda is very beautiful and fun to just ride around on motorized bikes.