Will this work?

[gtcway]

I'm planning on painting a boat and would like to use a surfacing primer to get a smooth finish. I've come across some Evercoat products Feather Fill and Slick Sand. They're polyester based and use MEKP as a hardener. Anyone have any experience with them on a gelcoat surface? I'm thinking that it is a cheaper alternative to a high build epoxy primer.
While I'm asking, I also do some fiberglass repairs on boats and think this will be a good product to use prior to spraying gelcoat to have a smooth seamless repair. Is there any reason I shouldn't?

Thanks.