[Descant]

First, Welcome to the Forum.
Sounds like we're talking pre-mix vs. additive put in each time you fuel up. It's always been a little bit of an irritant for me that we are forced to buy ethanol, and then forced to buy an additive to protect the engine from the ethanol. Recall the top notch choices from the EPA over MtBE?
The instructions on Startron suggest varying the amount of additive depending on anticipated use/non-use. Maybe you need it in the spring, not in the summer, and double dose for winter storage. If you buy pre-mix, you're paying for it all the time.
A couple of other Q & A: MVYC sells additive and asks if you want it when you fill up. No pre-mix.
Check the storage tank for water twice a year? When I worked for Irwin Marine, decades ago part of opening every morning was to check the tanks for water as they had time to settle overnight. In my book, a daily check is easy enough. Why wait for mid-season to find a problem?
I keep thinking we'll see more diesels on the lake, but still probably only a few; you can't tell by looking at a boat at the dock, but they don't need all this stuff. And no tune-ups.