We have been on the Katrin from Los Gigantes 3 times in 5 years. Always in February.
The first time was fantastic and we saw the pilot whales, which as already written look like large dolphins (to us amateur cetacean spotters!)
The second time we also saw the pilot whales, but it blew up very rough and we turned back early. It was a rough journey back to port, there weren't many of us on board, and we huddled at the back of the boat!
This year, they showed us dolphins which had gathered near the fish farms near the cliffs at Los Gigantes, we didn't go further out because they thought the weather would close in (remember it wasn't a very good winter there this year). The week before we were there, my sister had been in LG, and she said there were no boat trips all week.
I do believe that the captain and crew are very professional, and they have to decide whether to sail each day (which obviously they want to do, as it is their livelihood, and they want to show holiday-makers the whales etc.), then they have to decide how long to stay out at sea, depending on the weather conditions.
I suspect all the boats depend upon a spotter boat reporting back to them where the whales etc. are, it's fun to watch the Katrin and Flipper Uno set off in different directions and then converge on the whales...how do they do that humm??
In winter there's no point going on a long trip but I suspect on a calm day in summer it's nice to have the long trip and swim etc. as well.
Interesting point about the glass bottom boat, dozybint, we have been put off them since a boat trip in Majorca on a rough day, when you could see the sky through the glass bottom bit at times!