If one were in a production mode then price would be a consideration, for me at least.
The working time for mixed epoxy is easily adjusted by choosing which resin is used (fast, slow and slower).
BTW West Systems G-5 (their 5 minute epoxy) is NOT waterproof.
I've long heard that only epoxy sticks to epoxy but have never had that experience. There are 3 simple things to do in order to assure proper adhesion on epoxy. 1) If fully cured wipe with a damp cloth the aniline by-product which results from the curing process. 2) If fully cured rough up the surface with 80 grit paper after first having wiped with a damp cloth. 3) Best practice is to apply a second coat of epoxy before the first coat cures but after it is firm and still a bit sticky. This creates a chemical bond as opposed to a less desirable physical bond.
Epoxy resins w/o any FG cloth is much stronger than the brittle FG resin w/o FG cloth.
Mixing ratios of hardener to resin is much easier that drop-by-drop FG resin.
Epoxy resins are much stronger and more wear resistant than FG resins.
FG resins require the absence of oxygen
to fully cure. This is why one must use curing wax with FG resins.
West systems makes an epoxy, G-Flex, that is design to be used on plastic. It works great for this purpose.
Once you get the hang of using epoxy resin you'll never look back. After using West Systems epoxy for a few years I switched to Adtech resins which is approximately 2/3rds the price of West systems, they flow-out more smoothly and are a bit more flexible than West Systems. I order mine from a family business who are great folks to deal with, Expresscomposites.com.
These reasons are why I use epoxy as opposed to FG resins when making custom canoe paddles or for repairing canoes.