I bought a can and tried it. It works like it's supposed to -- it's a really thick paste that you can (kind of) smear on with a brush. However, I got just as good results from 3M's strip caulk and from regular exterior-grade paintable caulk from HD/Lowe's, with less mess. I'd say use it if you're going for a period-correct restoration, otherwise there's other alternatives that will be easier to remove later if necessary.
Just my .02