The good thing about Smooth On, or other quality epoxies is that they have a long shelf life. You will be using it in plenty of other bowmaking tasks, or other general woodworking projects, so you won't be wasting your money. I have had cheaper hardware store 24hr epoxy start to delaminate on splices.
TB3 will work, and work well, but the joinery needs to have much closer tolerances than what you can get away with epoxy.