The primary problem with alcohol in marine gasoline is that the alcohol can pull humidity out of the air. That is usually not a problem in most environments especially when frequent use requires fresh fuel to be added on a regular basis. But in the 100% humidity environment that a boat's fuel tank usually lives in, it can be a big problem. And infrequent use, stale fuel, metal containers, and low fuel levels significantly compound the problem.

In all of our small engines, we started using the gas substitutes a few years ago. It's more expensive than gasoline so we start using it late in the season as a run up to storage in stuff that gets run regularly. In the chain saws and stuff that only get run once in a while, we use it exclusively. Doing that has virtually eliminated our fuel related issues in those items.