We took the whale watching tour for the last day of our honeymoon after 2 weeks in Hawaii and 5 days in Seattle. We really wanted to go whale watching and the reason we booked with this company was that they offer a whale watch + return flight from Seattle. The sea plane flight from Lake Union was a wonderful experience. Whilst Friday Harbor is lovely, you don't need to book the early flight and spend the whole day there. There is still plenty of time in the afternoon (2-3 hours) if you book the 11am flight. We were met at the dock by the tour guide as our plane was a little late.
The highlight of the day was the whale watching tour - we saw plenty of orcas and other wildlife (seals, bald eagles, porpoises). This was such a great day, it is up there as one our best life experiences! All with gorgeous views in the background. There are plenty of other cruises, but the staff made this a really easy experience to book and enjoy. Any questions just email them. The staff on the boat are great, some of whom are on University summer placements are very knowledgeable and enthusiastic.
P.s. Take extra clothes, including hats and gloves. It can get windy and cold, despite the sunny weather. They have blankets, but extra clothing still required at times! Also sun cream and snacks! A camera with a good zoom is great. But to be honest, you can spend half your time trying to get the right photo, you miss things!