We've done it twice and love it (although getting up at 4am Pacific Time is a pain).
We did not share the cruise. The boats hold 10 but IMO all 10 spots do not have equal viewing and I like having my choice of seat!!! We did it once as a group of 4 and once as a group of 6.
Also, make sure to budget in the tip for the boat captain in the cost of your excursion.