actually keystone is one maker that recommends silicone on side surfaces. I'd never use it on a roof, use dicor there. I've used proflex and don't doubt its sealing capabilities but it's way too hard to apply and comes out too tacky already from the tube. And don't get it on your finger unless you wanna scrub your first layer of skin off to remove it! different strokes, but biscuit must be a an old pro with caulk gun, because when I used proflex it just keeps coming out of the tube even when the gun pusher is pulled back. Even though more expensive than regular silicone tubes, I use the smaller hand tubes rather than a gun tube as it's easier to operate and control flow. I'd say try both Sidney, and see what you like