Fiberglass (FRP) is merely epoxy adhesive with a glass weave or strand incorporated into it to create a structural element rather than simply bonding 2 things together. Adhesives called epoxies are mostly 2 part systems....resin plus hardener or catalyst. There are many...many types of epoxies that vary in strength and intended use. So, when you buy a fiberglass kit you're getting epoxy and the glass. Or you can buy them separate. I agree with one of the other replies to your post that the difference that may be in cost may be so small that you are better off getting the epoxy adhesive for repairs of joints. Usually, making a section of fiberglass requires more epoxy than a bonded joint...depending on how many layers of glass are used.