JB Weld is a consumer quality epoxy. Nothing special but does a good job in most cases. There are many industrial quality epoxy adhesives that are far superior to the JB Weld class of products. I have never used the Belzona brand but I have used Devcon
Liquid Steel and I can attest it is an incredible product. Cures much harder than JB or other common epoxies, super strong bond, totally machinable, adequate for replacing broken pieces on equipment, even for repairing stripped threads. It is sold at industrial supply stores and steel warehouse stores.
They also sell titanium, aluminum, stainless, bronze, and ceramic filled epoxies with similar superior physical properties. It is quite expensive but worth the price where you need the best.